Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2018	Feb. 22, 2019	Jun. 29, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Entity Registrant Name	MACROGENICS INC
Entity Central Index Key	0001125345
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		48,780,321
Entity Public Float			$ 842.5

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 220,128	$ 211,727
Marketable securities	12,735	93,394
Accounts receivable	29,583	13,643
Prepaid expenses	6,406	3,151
Other current assets	272	383
Total current assets	269,124	322,298
Property, equipment and software, net	56,712	49,983
Other assets	6,294	1,602
Total assets	332,130	373,883
Current liabilities:
Accounts payable	4,005	2,451
Accrued expenses	33,021	38,581
Deferred revenue	21,721	7,202
Deferred rent	1,018	1,048
Other current liabilities	175	473
Total current liabilities	59,940	49,755
Deferred revenue, net of current portion	19,001	13,637
Deferred rent, net of current portion	10,312	11,253
Total liabilities	89,253	74,645
Stockholders' equity:
Common stock, $0.01 par value -- 125,000,000 shares authorized, 42,353,301 and 36,859,077 shares outstanding at December 31, 2018 and December 31, 2017, respectively	424	369
Additional paid-in capital	732,727	611,270
Accumulated other comprehensive loss	(3)	(61)
Accumulated deficit	(490,271)	(312,340)
Total stockholders' equity	242,877	299,238
Total liabilities and stockholders' equity	$ 332,130	$ 373,883

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	125,000,000	125,000,000
Common stock, shares outstanding (in shares)	42,353,301	36,859,077

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Revenues	$ 60,121	$ 157,742	$ 91,880
Costs and expenses:
Research and development	190,827	147,232	122,091
General and administrative	40,500	32,653	29,831
Total costs and expenses	231,327	179,885	151,922
Loss from operations	(171,206)	(22,143)	(60,042)
Other income	(247)	2,517	1,514
Net loss	(171,453)	(19,626)	(58,528)
Other comprehensive loss:
Unrealized loss on investments	58	21	(77)
Comprehensive loss	$ (171,395)	$ (19,605)	$ (58,605)
Basic and diluted net loss per common share (in usd per share)	$ (4.19)	$ (0.54)	$ (1.69)
Basic and diluted weighted average number of common shares	40,925,318	36,095,080	34,685,274
Revenue from collaborative agreements
Revenues:
Revenues	$ 58,644	$ 155,516	$ 86,582
Revenue from government agreements
Revenues:
Revenues	$ 1,477	$ 2,226	$ 5,298

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss
Balance at Dec. 31, 2015	$ 313,337	$ 343	$ 0	$ 547,185	$ (234,186)	$ (5)
Balance (in shares) at Dec. 31, 2015		34,345,754	0
Share-based compensation	12,165			12,165
Stock plan related activity	1,854	$ 6	$ (39)	1,887
Stock plan related activity (in shares)		524,853	1,862
Retirement of treasury stock	0		$ 39	(39)
Retirement of treasury stock (in shares)			(1,862)
Unrealized gain on investments	(77)					(77)
Net loss	(58,528)				(58,528)
Balance at Dec. 31, 2016	268,751	$ 349	$ 0	561,198	(292,714)	(82)
Balance (in shares) at Dec. 31, 2016		34,870,607	0
Share-based compensation	14,744			14,744
Issuance of common stock, net of offering costs	34,244	$ 17		34,227
Issuance of common stock, net of offering costs (in shares)		1,699,284
Stock plan related activity	1,104	$ 3	$ (40)	1,141
Stock plan related activity (in shares)		289,186	1,862
Retirement of treasury stock	0		$ 40	(40)
Retirement of treasury stock (in shares)			(1,862)
Unrealized gain on investments	21					21
Net loss	(19,626)				(19,626)
Balance at Dec. 31, 2017	299,238	$ 369	$ 0	611,270	(312,340)	(61)
Balance (in shares) at Dec. 31, 2017		36,859,077	0
Cumulative effect of adoption of accounting standards					(6,478)
Share-based compensation	16,520			16,520
Issuance of common stock, net of offering costs	103,259	$ 52		103,207
Issuance of common stock, net of offering costs (in shares)		5,175,000
Stock plan related activity	1,733	$ 3	$ (260)	1,990
Stock plan related activity (in shares)		319,224	11,070
Retirement of treasury stock	0		$ 260	(260)
Retirement of treasury stock (in shares)			(11,070)
Unrealized gain on investments	58					58
Net loss	(171,453)				(171,453)
Balance at Dec. 31, 2018	242,877	$ 424	$ 0	$ 732,727	$ (490,271)	$ (3)
Balance (in shares) at Dec. 31, 2018		42,353,301	0
Cumulative effect of adoption of accounting standards	$ (6,478)

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net loss	$ (171,453)	$ (19,626)	$ (58,528)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization expense	8,279	7,228	7,608
Share-based compensation	16,520	14,744	12,165
Changes in operating assets and liabilities:
Accounts receivable	(15,941)	(10,878)	(1,540)
Prepaid expenses	(3,255)	332	(1,677)
Other assets	(4,580)	262	276
Accounts payable	1,554	(1,544)	2,232
Accrued expenses	3,506	12,832	4,659
Deferred revenue	13,405	6,533	(4,191)
Deferred rent	(971)	6,115	(1,134)
Other liabilities	(298)	(1,593)	(3,549)
Net cash provided by (used in) operating activities	(153,234)	14,405	(43,679)
Cash flows from investing activities
Purchases of marketable securities	(132,750)	(135,122)	(347,762)
Proceeds from sales and maturities of marketable securities	214,348	242,401	288,894
Purchases of property, equipment and software	(24,954)	(29,403)	(11,381)
Net cash provided by (used in) investing activities	56,644	77,876	(70,249)
Cash flows from financing activities
Proceeds from issuance of common stock, net of offering costs	103,259	34,244	0
Proceeds from stock option exercises and ESPP purchases	1,992	1,144	1,893
Purchase of treasury stock	(260)	(40)	(39)
Net cash provided by financing activities	104,991	35,348	1,854
Net change in cash and cash equivalents	8,401	127,629	(112,074)
Cash and cash equivalents at beginning of period	211,727	84,098	196,172
Cash and cash equivalents at end of period	220,128	211,727	84,098
Non-cash operating and investing activities:
Fair value of warrants received	$ 6,130	$ 0	$ 0

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Basis of Presentation and Principles of Consolidation

The consolidated financial statements include the accounts of MacroGenics, Inc. and its wholly owned subsidiary, MacroGenics UK Limited. All intercompany accounts and transactions have been eliminated in consolidation. The Company currently operates in one operating segment. Operating segments are defined as components of an enterprise about which separate discrete information is available for the chief operating decision maker, or decision making group, in deciding how to allocate resources and assessing performance. The Company views its operations and manages its business in one segment, which is developing monoclonal antibody-based therapeutics for cancer, autoimmune and infectious diseases.

Use of Estimates

The preparation of the financial statements in accordance with generally accepted accounting principles (GAAP) requires the Company to make estimates and judgments in certain circumstances that affect the reported amounts of assets, liabilities, revenues and expenses, and related disclosure of contingent assets and liabilities. In preparing these consolidated financial statements, management has made its best estimates and judgments of certain amounts included in the financial statements, giving due consideration to materiality. On an ongoing basis, the Company evaluates its estimates, including those related to revenue recognition, fair values of assets, stock-based compensation, income taxes, preclinical study and clinical trial accruals and other contingencies. Management bases its estimates on historical experience or on various other assumptions that it believes to be reasonable under the circumstances. Actual results could differ from these estimates.

Cash, Cash Equivalents and Marketable Securities

The Company considers all investments in highly liquid financial instruments with a maturity of 90 days or less at the date of purchase to be cash equivalents. Cash and cash equivalents includes investments in money market funds with commercial banks and financial institutions, securities issued by the U.S. government and its agencies, Government Sponsored Enterprise agency debt obligations and corporate debt obligations. Cash equivalents are stated at amortized cost, plus accrued interest, which approximates fair value.

The Company carries marketable securities classified as available-for-sale at fair value as determined by prices for identical or similar securities at the balance sheet date. Marketable securities consist of Level 2 financial instruments in the fair-value hierarchy. The Company records unrealized gains and losses as a component of other comprehensive loss within the statements of operations and comprehensive loss and as a separate component of stockholders' equity. Realized gains or losses on available-for-sale securities are determined using the specific identification method and the Company includes net realized gains and losses in other income (expense).

At each balance sheet date, the Company assesses available-for-sale securities in an unrealized loss position to determine whether the unrealized loss is other-than-temporary. The Company considers factors including: the significance of the decline in value compared to the cost basis, underlying factors contributing to a decline in the prices of securities in a single asset class, the length of time the market value of the security has been less than its cost basis, the security's relative performance versus its peers, sector or asset class, expected market volatility and the market and economy in general. The Company also evaluates whether it is more likely than not that it will be required to sell a security prior to recovery of its fair value. An impairment loss is recognized at the time the Company determines that a decline in the fair value below its cost basis is other-than-temporary. There were no unrealized losses at December 31, 2018 or 2017 that the Company determined to be other-than-temporary.

Accounts Receivable

Accounts receivable that management has the intent and ability to collect are reported in the consolidated balance sheets at outstanding amounts, less an allowance for doubtful accounts. The Company writes off uncollectible receivables when the likelihood of collection is remote.

The Company evaluates the collectability of accounts receivable on a regular basis. The allowance, if any, is based upon various factors including the financial condition and payment history of customers, an overall review of collections experience on other accounts and economic factors or events expected to affect future collections experience. No allowance was recorded as of December 31, 2018 or 2017, as the Company has a history of collecting on all outstanding accounts.

Fair Value of Financial Instruments

The Company's financial instruments consist of cash and cash equivalents, marketable securities, accounts receivable, accounts payable and accrued expenses. The carrying amount of accounts receivable, accounts payable and accrued expenses are generally considered to be representative of their respective fair values because of their short-term nature. The Company accounts for recurring and non-recurring fair value measurements in accordance with the Financial Accounting Standards Board (FASB) Accounting Standards Codification (ASC) 820, Fair Value Measurements and Disclosures (ASC 820). ASC 820 defines fair value, establishes a fair value hierarchy for assets and liabilities measured at fair value, and requires expanded disclosures about fair value measurements. The ASC 820 hierarchy ranks the quality of reliability of inputs, or assumptions, used in the determination of fair value and requires assets and liabilities carried at fair value to be classified and disclosed in one of the following three categories:

•Level 1 – Fair value is determined by using unadjusted quoted prices that are available in active markets for identical assets and liabilities.

•Level 2 – Fair value is determined by using inputs other than Level 1 quoted prices that are directly or indirectly observable. Inputs can include quoted prices for similar assets and liabilities in active markets or quoted prices for identical assets and liabilities in inactive markets. Related inputs can also include those used in valuation or other pricing models, such as interest rates and yield curves that can be corroborated by observable market data.

•Level 3 – Fair value is determined by inputs that are unobservable and not corroborated by market data. Use of these inputs involves significant and subjective judgments to be made by a reporting entity – e.g., determining an appropriate adjustment to a discount factor for illiquidity associated with a given security.

The Company evaluates financial assets and liabilities subject to fair value measurements on a recurring basis to determine the appropriate level at which to classify them each reporting period. This determination requires the Company to make subjective judgments as to the significance of inputs used in determining fair value and where such inputs lie within the ASC 820 hierarchy.

Financial assets measured at fair value on a recurring basis were as follows (in thousands):


	Fair Value Measurement at December 31, 2018
			Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds	$	46,257	$	46,257	$	—	$	—
U.S Treasury securities	12,488		—		12,488		—

Corporate debt securities	100,214		—		100,214		—
Common stock warrants	1,890		—		—		$	1,890
Total assets measured at fair value ^(a)	$	160,849	$	46,257	$	112,702	$	1,890


	Fair Value Measurement at December 31, 2017
			Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds	$	61,512	$	61,512	$	—	$	—
U.S Treasury securities	3,989		—		3,989		—
Government-sponsored enterprises	11,991		—		11,991		—
Corporate debt securities	78,418		—		78,418		—
Total assets measured at fair value ⁽^b)	$	155,910	$	61,512	$	94,398	$	—

(a) Total assets measured at fair value at December 31, 2018 includes approximately $146.2 million reported in cash and cash equivalents on the balance sheet.

(b) Total assets measured at fair value at December 31, 2017 includes approximately $62.5 million reported in cash and cash equivalents on the balance sheet.

The fair value of Level 2 securities is determined from market pricing and other observable market inputs for similar securities obtained from various third-party data providers. These inputs either represent quoted prices for similar assets in active markets or have been derived from observable market data. The fair value of Level 3 securities is determined using the Black-Scholes option-pricing model. There were no transfers between levels during the periods presented.

Concentration of Credit Risk

Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash, cash equivalents, marketable securities and accounts receivable. The Company maintains its cash and money market funds with financial institutions that are federally insured. While balances deposited in these institutions often exceed Federal Deposit Insurance Corporation limits, the Company has not experienced any losses on related accounts to date. The Company's investment policy limits investments to certain types of debt securities issued by the U.S. government, its agencies and institutions with investment-grade credit ratings and places restrictions on maturities and concentration by type and issuer. The counterparties are various corporations, financial institutions and government agencies of high credit standing.

The Company's revenue relates to agreements with various collaborators and contracts and research grants received from U.S. government agencies. The following table includes those collaborators that represent more than 10% of total revenue earned in the periods indicated:


	Year Ended December 31,
	2018	2017		2016
Incyte Corporation (Incyte)	68%	96	%	—%
Janssen Biotech, Inc. (Janssen)	*	*		85%

Provention Bio, Inc. (Provention)	10%	—%		—%

The following table includes those counterparties that represent more than 10% of accounts receivable at the date indicated:


	December 31,
	2018	2017
Zai Lab Limited (Zai Lab)	76%	—%
Incyte	16%	—%
F. Hoffmann-La Roche Ltd and Hoffmann-La Roche Inc. (Roche)	—%	73%
Les Laboratoires Servier and Institut de Recherches Servier (Servier)	*	12%

* Balance is less than 10%

Property, Equipment and Software

Property, equipment and software are stated at cost. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation or amortization are removed from the accounts and any resulting gain or loss is credited or charged to operations. Repairs and maintenance costs are expensed as incurred. Depreciation and amortization are computed using the straight-line method over the following estimated useful lives:


Computer equipment			3 years
Software			3 years
Furniture			10 years
Laboratory and office equipment			5 years
Leasehold improvements			Shorter of lease term or useful life

Impairment of Long-Lived Assets

The Company assesses the recoverability of its long-lived assets in accordance with the provisions of ASC 360, Property, Plant and Equipment. ASC 360 requires that long-lived assets be reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of the long-lived asset is measured by a comparison of the carrying amount of the asset to future undiscounted net cash flows expected to be generated by the asset or asset group. If carrying value exceeds the sum of undiscounted cash flows, the Company then determines the fair value of the underlying asset group. Any impairment to be recognized is measured by the amount by which the carrying amount of the asset group exceeds the estimated fair value of the asset group. Assets to be disposed of are reported at the lower of the carrying amount or fair value, less costs to sell. For the years ended December 31, 2018, 2017 and 2016, the Company determined that there were no impaired assets.

Income Taxes

Deferred tax assets and liabilities are determined based on differences between the financial reporting and tax basis of assets and liabilities and are measured using the enacted tax rates and laws that are expected to be in effect when the differences are expected to reverse. The effect on deferred tax assets and liabilities of a change in tax rates is recognized as income in the period that such tax rate changes are enacted. The measurement of a deferred tax asset is reduced, if necessary, by a valuation allowance if it is more likely than not that some portion or all of the deferred tax asset will not be realized. Financial statement recognition of a tax position taken or expected to be taken in a tax return is determined based on a more-likely-than-not threshold of that position being sustained. If the tax position meets this threshold, the benefit to be recognized is measured as the largest amount that is more likely than not to be realized upon ultimate settlement. The Company's policy is to record interest and penalties related to uncertain tax positions as a component of income tax expense.

Revenues

Beginning on January 1, 2018, the Company recognizes revenue under Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers and all related amendments (collectively ASC 606) when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied.

The Company enters into licensing agreements that are within the scope of ASC 606, under which it may license rights to research, develop, manufacture and commercialize its product candidates to third parties. The terms of these arrangements typically include payment to the Company of one or more of the following: non-refundable, upfront license fees; reimbursement of certain costs; customer option exercise fees; development, regulatory and commercial milestone payments; and royalties on net sales of licensed products. The Company may also enter into development and manufacturing service agreements with its collaborators.

For each arrangement that results in revenues, the Company identifies all performance obligations, which may include a license to intellectual property and know-how, research and development activities, transition activities and/or manufacturing services. In order to determine the transaction price, in addition to any upfront payment, the Company estimates the amount of variable consideration at the outset of the contract either utilizing the expected value or most likely amount method, depending

on the facts and circumstances relative to the contract. The Company constrains (reduces) the estimates of variable consideration such that it is probable that a significant reversal of previously recognized revenue will not occur. When determining if variable consideration should be constrained, management considers whether there are factors outside the Company’s control that could result in a significant reversal of revenue. In making these assessments, the Company considers the likelihood and magnitude of a potential reversal of revenue. These estimates are re-assessed each reporting period as required.

Once the estimated transaction price is established, amounts are allocated to the performance obligations that have been identified. The transaction price is generally allocated to each separate performance obligation on a relative standalone selling price basis. The Company must develop assumptions that require judgment to determine the standalone selling price in order to account for these agreements. To determine the standalone selling price, the Company’s assumptions may include (i) the probability of obtaining marketing approval for the product candidate, (ii) estimates regarding the timing and the expected costs to develop and commercialize the product candidate, and (iii) estimates of future cash flows from potential product sales with respect to the product candidate. Standalone selling prices used to perform the initial allocation are not updated after contract inception. The Company does not include a financing component to its estimated transaction price at contract inception unless it estimates that certain performance obligations will not be satisfied within one year.

Amounts received prior to revenue recognition are recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current portion of deferred revenue in the accompanying consolidated balance sheets. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion.

Licenses. If the license to the Company’s intellectual property is determined to be distinct from the other promises or performance obligations identified in the arrangement, the Company recognizes revenue from non-refundable, upfront fees allocated to the license when the license is transferred to the customer and when (or as) the customer is able to use and benefit from the license. In assessing whether a promise or performance obligation is distinct from the other promises, the Company considers factors such as the research, development, manufacturing and commercialization capabilities of the licensee and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the licensee can benefit from a promise for its intended purpose without the receipt of the remaining promise, whether the value of the promise is dependent on the unsatisfied promise, whether there are other vendors that could provide the remaining promise, and whether it is separately identifiable from the remaining promise. For licenses that are combined with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The measure of progress, and thereby periods over which revenue should be recognized, are subject to estimates by management and may change over the course of the research and development and licensing agreement. Such a change could have a material impact on the amount of revenue the Company records in future periods.

Research, Development and/or Manufacturing Services. The promises under the Company’s agreements may include research and development or manufacturing services to be performed by the Company on behalf of the counterparty. If these services are determined to be distinct from the other promises or performance obligations identified in the arrangement, the Company recognizes the transaction price allocated to these services as revenue over time based on an appropriate measure of progress when the performance by the Company does not create an asset with an alternative use and the Company has an enforceable right to payment for the performance completed to date. If these services are determined not to be distinct from the other promises or performance obligations identified in the arrangement, the Company recognizes the transaction price allocated to the combined performance obligation as the related performance obligations are satisfied.

Customer Options. If an arrangement contains customer options, the Company evaluates whether the options are material rights because they allow the customer to acquire additional goods or services for free or at a discount. If the customer options are determined to represent a material right, the material right is recognized as a separate performance obligation at the outset of the arrangement. The Company allocates the transaction price to material rights based on the relative standalone selling price, which is determined based on the identified discount and the probability that the customer will exercise the option. Amounts allocated to a material right are not recognized as revenue until, at the earliest, the option is exercised. If the options are deemed not to be a material right, they are excluded as performance obligations at the outset of the arrangement.

Milestone Payments. At the inception of each arrangement that includes development milestone payments, the Company evaluates whether the milestones are considered probable of being achieved and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not

occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The Company evaluates factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to achieve the particular milestone in making this assessment. There is considerable judgment involved in determining whether it is probable that a significant revenue reversal would not occur. At the end of each subsequent reporting period, the Company reevaluates the probability of achievement of all milestones subject to constraint and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment.

Royalties. For arrangements that include sales-based royalties which are the result of a customer-vendor relationship and for which the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied or partially satisfied. To date, the Company has not recognized any royalty revenue resulting from any of its licensing arrangements.

The Company analyzes its collaboration arrangements to assess whether such arrangements involve joint operating activities performed by parties who are both active participants in the activities and are both exposed to significant risks and rewards dependent on the commercial success of such activities. Such arrangements generally are within the scope of ASC 808, Collaborative Arrangements (ASC 808). While ASC 808 defines collaborative arrangements and provides guidance on income statement presentation, classification, and disclosures related to such arrangements, it does not address recognition and measurement matters, such as (1) determining the appropriate unit of accounting or (2) when the recognition criteria are met. Therefore, the accounting for these arrangements is either based on an analogy to other accounting literature or an accounting policy election by the Company. The Company accounts for certain components of the collaboration agreement that are reflective of a vendor-customer relationship (e.g., licensing arrangement) based on an analogy to ASC 606. The Company accounts for other components based on a reasonable, rational and consistently applied accounting policy election. Reimbursements from the counter-party that are the result of a collaborative relationship with the counter-party, instead of a customer relationship, such as co-development activities, are recorded as a reduction to research and development expense as the services are performed.

For a complete discussion of accounting for revenue from collaborative and other agreements, see Note 8, Collaboration and Other Agreements.

Research and Development Costs

Research and development expenditures are expensed as incurred. Research and development costs primarily consist of employee related expenses, including salaries and benefits, expenses incurred under agreements with contract research organizations, investigative sites and consultants that conduct the Company's clinical trials, the cost of acquiring and manufacturing clinical trial materials and other allocated expenses, license fees for and milestone payments related to in-licensed products and technologies, stock-based compensation expense, and costs associated with non-clinical activities and regulatory approvals.

Right-to-develop agreements may contain cost-sharing provisions whereby the Company and the collaborator share the cost of research and development activities. Reimbursement of research and development expenses received in connection with these agreements is recorded as a reduction of such expenses.

Comprehensive Loss

Comprehensive loss represents net loss adjusted for the change during the periods attributed to unrealized gains and losses on available-for-sale securities.

Stock-based Compensation

Stock-based payments are accounted for in accordance with the provisions of ASC 718, Compensation – Stock Compensation. The fair value of stock-based payments is estimated, on the date of grant, using the Black-Scholes model. The resulting fair value is recognized ratably over the requisite service period, which is generally the vesting period of the option.

For all time-vesting awards granted, expense is amortized using the straight-line attribution method. For awards that contain a performance condition, expense is amortized using the accelerated attribution method. Recognition of stock-based compensation expense is based on the value of the portion of stock-based awards that is ultimately expected to vest during the period.

The Company utilizes the Black-Scholes model for estimating fair value of its stock options granted. Option valuation models, including the Black-Scholes model, require the input of highly subjective assumptions, and changes in the assumptions used can materially affect the grant-date fair value of an award. These assumptions include the risk-free rate of interest, expected dividend yield, expected volatility and the expected life of the award.

Net Loss Per Share

Basic loss per common share is determined by dividing loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration of common stock equivalents. Diluted loss per share is computed by dividing the loss attributable to common stockholders by the weighted-average number of common share equivalents outstanding for the period. The treasury stock method is used to determine the dilutive effect of the Company's stock option grants. 5,273,964 stock options (common stock equivalents) were excluded from the calculation of diluted net loss per share for the year ended December 31, 2018 because their inclusion would have been anti-dilutive. 4,504,642 stock options and 3,838,060 stock options were excluded from the calculation of diluted net loss per share for the years ended December 31, 2017 and 2016, respectively, because their inclusion would have been anti-dilutive.

Recently Adopted Accounting Standards

In May 2014, the FASB issued ASC 606. The Company adopted ASC 606 on January 1, 2018 using the modified retrospective method for all contracts that were not completed as of January 1, 2018. For contracts that were modified before the effective date, the Company reflected the aggregate effect of all modifications when identifying performance obligations and allocating transaction price in accordance with available practical expedients. Comparative prior period information continues to be reported under the accounting standards in effect for the period presented.

As a result of applying the modified retrospective method to adopt the new guidance, the following adjustments were made to accounts on the consolidated balance sheet as of January 1, 2018 (in thousands):


	Pre-Adoption		ASC 606 Adjustment		Post-Adoption
Deferred revenue, current	$	7,202	$	540	$	7,742
Deferred revenue, net of current portion	13,637		5,939		19,576
Accumulated deficit	(312,340)		(6,478)		(318,818)

The transition adjustment resulted primarily from changes in the pattern of revenue recognition for upfront fees and license grant fees.

The following table shows the impact of adoption to the consolidated statement of income and balance sheet (in thousands):


	Year Ended December 31, 2018
	As Reported		Balances Without Adoption of ASC 606		Effect of Change Higher/(Lower)
Revenue from collaborative agreements	$	58,644	$	58,104	$	540
Net loss	(171,453)		(171,993)		(540)
Basic and diluted net loss per common share	$	(4.19)	$	(4.20)	$	0.01

	As of December 31, 2018
	As Reported		Balances Without Adoption of ASC 606		Effect of Change Higher/(Lower)
Deferred revenue, current	$	21,721	$	22,210	$	(489)
Deferred revenue, net of current portion	19,001		12,573		6,428
Accumulated deficit	(490,271)		$	(484,332)	$	(5,939)

The following table presents changes in the Company’s contract liabilities during the year ended December 31, 2018 (in thousands):


	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
Deferred revenue (current and non-current)	$	27,318	$	22,992	$	(9,588)	$	40,722

During the year ended December 31, 2018, the Company recognized $9.6 million in revenue as a result of changes in the contract liability balance.

In May 2017, the FASB issued ASU 2017-09, Compensation – Stock Compensation (Topic 718): Scope Modification Accounting. The new standard is intended to reduce the diversity in practice and cost and complexity when applying the guidance in Topic 718 to a change to the terms or conditions of a share-based payment award. The new standard was effective beginning January 1, 2018. The adoption of this standard did not have a material impact on the Company’s financial position or results of operations upon adoption.

On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (the Tax Act) was signed into law making significant changes to the Internal Revenue Code, which included how the U.S. imposes income tax on multinational corporations. Key changes in the Tax Act which are relevant to the Company, and generally effective January 1, 2018, include a flat corporate income tax rate of 21% to replace the marginal rates that range from 15% to 35% and the elimination of the corporate alternative minimum tax. The Tax Act also imposes limits on executive compensations and interest expense deductions, while permitting the immediate expensing for the cost of new investments in certain property acquired after September 27, 2017.

On December 22, 2017, the SEC issued Staff Accounting Bulletin No. 118 (SAB 118) to address the application of U.S. GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Tax Act. SAB 118 allowed registrants to include a provisional amount to account for the implications of the Tax Act where a reasonable estimate can be made and required the completion of the accounting no later than one year from the date of the enactment of the Tax Act, or December 22, 2018. The Company has recognized the provisional tax impacts related to the re-measurement of its U.S. deferred tax assets and liabilities to 21% in 2017 and included these amounts in its consolidated financial statements for the year ended December 31, 2017. This change in value of these deferred tax assets and liabilities was offset by a corresponding change in valuation allowance, thus no tax expense or benefit was recorded. The Company completed its evaluation of the effects of the Tax Act during the fourth quarter of 2018, and the provisional amounts the Company accounted for in its December 31, 2017 provision were finalized with no adjustments.

Recently Issued Accounting Standards

In February 2016, the FASB issued ASU No. 2016-02, Leases (ASU 2016-02) that provides principles for the recognition, measurement, presentation and disclosure of leases for both lessees and lessors. ASU 2016-02 requires a lessee to recognize assets and liabilities on the balance sheet for operating leases and changes many key definitions, including the definition of a lease. ASU 2016-02 includes a short-term lease exception for leases with an original term of 12 months or less, in which a lessee can make an accounting policy election not to recognize lease assets and lease liabilities. Lessees will continue to differentiate between finance leases (previously referred to as capital leases) and operating leases, using classification criteria that are substantially similar to the previous guidance. Originally, entities were required to adopt ASU 2016-02 using a modified retrospective transition approach for all leases existing at, or entered into after, the date of initial application. However, in July 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements, which now allows entities the option of recognizing the cumulative effect of applying the new standard as an adjustment to the opening balance of retained earnings in the year of adoption while continuing to present all prior periods under previous lease accounting guidance. In July 2018, the FASB also issued ASU 2018-10, Codification Improvements to Topic 842, Leases, which clarifies how to apply certain aspects of ASU 2016-02. ASU 2016-02, ASU 2018-10 and ASU 2018-11 (now commonly referred to as ASC Topic 842 (ASC 842)) is effective for the Company’s fiscal year beginning January 1, 2019. Although early adoption is permitted, the Company has not elected to do so. The Company plans to elect the transition option provided under ASU 2018-11, which will not require adjustments to comparative periods nor require modified disclosures in those comparative periods. Upon adoption, the Company expects to elect the transition package of practical expedients permitted within the new standard, which among other things, allows the carryforward of the historical lease classification. Based on its current lease portfolio, the Company estimates that the adoption ASC 842 will result in approximately $16.0 million of right of use assets and $28.0 million of lease liabilities being reflected on its consolidated balance sheet at the date of adoption.

In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808)—Clarifying the interaction between Topic 808 and Topic 606 (ASU 2018-18). The amendments provide guidance on whether certain

transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606. It also specifically (i) addresses when the participant should be considered a customer in the context of a unit of account, (ii) adds unit-of-account guidance in ASC 808 to align with guidance in ASC 606, and (iii) precludes presenting revenue from a collaborative arrangement together with revenue recognized under ASC 606 if the collaborative arrangement participant is not a customer. The guidance will be effective for fiscal years beginning after December 15, 2019. Early adoption is permitted and should be applied retrospectively. The Company does not anticipate the adoption of this standard will have a material impact on its consolidated financial statements.

The Company has evaluated all other ASUs issued through the date the consolidated financials were issued and believes that the adoption of these will not have a material impact on the Company's consolidated financial statements.

Marketable Securities

12 Months Ended

Dec. 31, 2018

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

Available-for-sale marketable securities as of December 31, 2018 and 2017 were as follows (in thousands):


	December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value


Corporate debt securities	$	12,738	$	—	$	(3)	$	12,735


	December 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
U.S. Treasury securities	$	3,995	$	—	$	(6)	$	3,989
Government-sponsored enterprises	11,998		—		(7)		11,991
Corporate debt securities	77,462		2		(50)		77,414
Total	$	93,455	$	2	$	(63)	$	93,394

All of the Company's available-for-sale securities held at December 31, 2018 and 2017 had maturity dates of less than one year.

All available-for-sale securities in an unrealized loss position as of December 31, 2018 and 2017 were in a loss position for less than twelve months. There were no unrealized losses at December 31, 2018 or 2017 that the Company determined to be other-than-temporary. The Company recorded interest income of $2.3 million, $2.4 million and $2.3 million during the years ended December 31, 2018, 2017 and 2016, respectively, which is included in other income (expense) on the consolidated statements of operations and comprehensive loss.

Property, Equipment and Software

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

Property, Equipment and Software

Property, Equipment and SoftwareProperty, equipment and software consists of the following (in thousands):


	December 31,
	2018		2017
Computer equipment	$	2,360	$	2,261
Software	7,011		5,111
Furniture and office equipment	668		656
Lab equipment	36,062		20,549
Leasehold improvements	48,328		17,525
Construction in progress	218		32,800
Property, equipment and software	94,647		78,902
Less accumulated depreciation and amortization	(37,935)		(28,919)
Property, equipment and software, net	$	56,712	$	49,983

Construction in progress at December 31, 2017 consisted of the costs incurred for the build-out of a manufacturing suite at the Company's headquarters building in Rockville, Maryland, which was completed in mid-2018.

We had $0.6 million in property, equipment and software at December 31, 2018 that was purchased in 2018 but was not paid for by year end. Property, equipment and software balance at December 31, 2017 includes approximately $9.6 million in assets that were purchased in 2017 but were not paid for by year end. Depreciation and amortization expense related to property, equipment and software for the years ended December 31, 2018, 2017 and 2016 was $9.2 million, $7.0 million and $6.8 million, respectively.

Stockholders' Equity	12 Months Ended
Stockholders' Equity	Dec. 31, 2018
Equity [Abstract]
Stockholders' Equity	Stockholders' Equity The Company's amended and restated certificate of incorporation authorizes 125,000,000 shares of common stock, and 5,000,000 shares of undesignated preferred stock, both with a par value of $.01 per share. There were no shares of undesignated preferred stock issued or outstanding as of December 31, 2018 or 2017. On April 26, 2017, the Company entered into a definitive agreement with an institutional healthcare investor to purchase 1,100,000 shares of its common stock at a purchase price of $21.50 per share in a registered direct offering. Proceeds to the Company, before deducting estimated offering expenses, were $23.7 million. The shares were offered pursuant to the Company’s effective shelf registration on Form S-3 that was filed with the SEC on November 2, 2016. On May 3, 2017, the Company entered into a sales agreement with an agent to sell, from time to time, shares of its common stock having an aggregate sales price of up to $75.0 million through an “at the market offering” (ATM Offering) as defined in Rule 415 under the Securities Act of 1933, as amended. The shares that may be sold under the sales agreement would be issued and sold pursuant to the Company's shelf registration statement on Form S-3 that was filed with the SEC on November 2, 2016. During the year ended December 31, 2017, the Company sold 599,284 shares of common stock resulting in net proceeds of $10.8 million related to the ATM Offering. On April 2, 2018, the Company completed a firm-commitment underwritten public offering, in which the Company sold 4,500,000 shares of its common stock at a price of $21.25 per share. Additionally, the underwriters of the offering exercised the full amount of their over-allotment option resulting in the sale of an additional 675,000 shares of the Company's common stock at a price of $21.25 per share. Upon closing, the Company received net proceeds of approximately $103.0 million from this offering, net of underwriting discounts and commissions and other offering expenses.

Stock-based Compensation

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-based Compensation

Employee Stock Purchase Plan

In May 2017, the Company’s stockholders approved the 2016 Employee Stock Purchase Plan (the 2016 ESPP). The 2016 ESPP is structured as a qualified employee stock purchase plan under Section 423 of the Internal Revenue Code of 1986, as amended, and is not subject to the provisions of the Employee Retirement Income Security Act of 1974. The Company reserved 800,000 shares of common stock for issuance under the 2016 ESPP. The 2016 ESPP allows eligible employees to purchase shares of the Company’s common stock at a discount through payroll deductions of up to 10% of their eligible compensation, subject to any plan limitations. The 2016 ESPP provides for six-month offering periods ending on May 31 and November 30 of each year. At the end of each offering period, employees are able to purchase shares at 85% of the fair market

value of the Company’s common stock on the last day of the offering period. During the year ended December 31, 2018, employees purchased 44,862 shares of common stock under the 2016 ESPP for net proceeds to the Company of approximately $0.8 million.

Employee Stock Option Plans

Effective February 2003, the Company implemented the 2003 Equity Incentive Plan (2003 Plan), and it was amended and approved by the Company's stockholders in 2005. Stock options granted under the 2003 Plan may be either incentive stock options as defined by the Internal Revenue Code (IRC), or non-qualified stock options. In 2013, the 2003 Plan was terminated, and no further awards may be issued under the plan. Any shares of common stock subject to awards under the 2003 Plan that expire, terminate, or are otherwise surrendered, canceled, forfeited or repurchased without having been fully exercised, or resulting in any common stock being issued, will become available for issuance under the 2013 Stock Incentive Plan (2013 Plan), up to a specified number of shares. As of December 31, 2018, under the 2003 Plan, there were options to purchase an aggregate of 746,803 shares of common stock outstanding at a weighted average exercise price of $2.03 per share.

In October 2013, the Company implemented the 2013 Plan. The 2013 Plan provides for the grant of stock options and other stock-based awards, as well as cash-based performance awards. The aggregate number of shares of common stock initially available for issuance pursuant to awards under the 2013 Plan was 1,960,168 shares. The number of shares of common stock reserved for issuance will automatically increase on January 1 of each year from January 1, 2014 through and including January 1, 2023, by the lesser of (a) 1,960,168 shares, (b) 4.0% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, or (c) the number of shares of common stock determined by the Board of Directors. During the year ended December 31, 2018, the maximum number of shares of common stock authorized to be issued by the Company under the 2013 Plan was increased to 8,244,131. If an option expires or terminates for any reason without having been fully exercised, if any shares of restricted stock are forfeited, or if any award terminates, expires or is settled without all or a portion of the shares of common stock covered by the award being issued, such shares are available for the grant of additional awards. However, any shares that are withheld (or delivered) to pay withholding taxes or to pay the exercise price of an option are not available for the grant of additional awards. As of December 31, 2018, under the 2013 Plan, there were options to purchase an aggregate of 4,527,161 shares of common stock outstanding at a weighted average exercise price of $25.56 per share.

The following stock-based compensation amounts were recognized for the periods indicated (in thousands):


	Year Ended December 31,
	2018		2017		2016

Research and development	$	7,919	$	7,388	$	5,778
General and administrative	8,601		7,356		6,387
Total stock-based compensation expense	$	16,520	$	14,744	$	12,165

Employee Stock Options

The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing model using the assumptions in the following table:


	Year Ended December 31,
	2018	2017	2016
Expected dividend yield	0%	0%	0%
Expected volatility	68% - 72%	67% - 68%	64% - 69%
Risk-free interest rate	2.4% - 3.1%	1.9% - 2.3%	1.2% - 2.4%
Expected term	6.25 years	6.25 years	6.25 years

Expected Dividend Yield – The Company has never declared or paid dividends and has no plans to do so in the foreseeable future.

Expected Volatility – Volatility is a measure of the amount by which a financial variable such as a share price has fluctuated (historical volatility) or is expected to fluctuate (expected volatility) during a period. As the Company does not yet have sufficient history of its own volatility, the Company has identified several public entities of similar size, complexity and stage of development and estimates volatility based on the volatility of these companies.

Risk-Free Interest Rate – This is the U.S. Treasury rate for the week of each option grant during the year, having a term that most closely resembles the expected life of the option.

Expected Term – This is the period of time that the options granted are expected to remain unexercised. Options granted have a maximum term of ten years. The Company uses a simplified method to calculate the average expected term.

In addition to the assumptions above, the Company estimates the forfeiture rate based on turnover data with further consideration given to the class of the employees to whom the options were granted. The forfeiture rate is the estimated percentage of options granted that is expected to be forfeited or canceled on an annual basis before becoming fully vested.

The following table summarizes stock option activity for 2018:


	Shares	Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2017	4,504,642	$	19.79	7.0
Granted	1,269,844	27.18
Options exercised	(285,432)	4.22
Forfeited or expired	(215,090)	24.43
Outstanding, December 31, 2018	5,273,964	22.23		6.8	$	7,969

December 31, 2018:
Exercisable	3,544,139	20.60		5.9	7,969
Vested and expected to vest	5,086,009	22.10		6.7	7,969

During 2018, 2017 and 2016 the Company issued 274,362, 253,036 and 526,715 net shares of common stock, respectively, in conjunction with stock option exercises. The Company received cash proceeds from the exercise of stock options of approximately $0.9 million, $0.5 million and $1.9 million during 2018, 2017 and 2016, respectively.

The weighted-average grant-date fair value of options granted during 2018, 2017 and 2016 was $17.90, $12.53 and $15.17 per share, respectively. The total intrinsic value of options exercised during 2018, 2017 and 2016 was approximately $5.2 million, $4.2 million and $10.8 million, respectively. The total fair value of stock options which vested during 2018, 2017 and 2016 was $16.4 million, $14.6 million and $11.6 million, respectively. As of December 31, 2018, the total unrecognized compensation expense related to non-vested stock options, net of related forfeiture estimates, was $24.2 million, which the Company expects to recognize over a weighted-average period of approximately 2.6 years.

Income Taxes

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Income Taxes

Income Taxes For the years ended December 31, 2018, 2017 and 2016 there was no provision for income taxes due to taxable losses generated, fully offset by a valuation allowance.

The significant components of the Company's deferred income tax assets (liabilities) were as follows (in thousands):


	December 31,
	2018		2017
Deferred income tax assets:
Federal U.S. net operating loss carryforward	$	87,284	$	50,346
State net operating loss carryforward	22,809		7,551
Research and development credit, net	29,750		21,284
Orphan drug credit, net	22,580		21,708
Deferred rent	3,118		3,385
Deferred revenue	3,736		2,982
Depreciation	—		155
Other	6,854		5,847
Gross deferred income tax assets	176,131		113,258
Valuation allowance	(172,457)		(112,453)
Net deferred income tax assets	3,674		805

Deferred income tax liabilities:
Depreciation	(1,911)		—
Prepaid expenditures	(1,763)		(805)
Gross deferred income tax liabilities	(3,674)		(805)
Net deferred income tax asset/(liability)	$	—	$	—

The Company recognizes valuation allowances to reduce deferred tax assets to the amount that is more likely than not to be realized. In assessing the likelihood of realization, management considers (i) future reversals of existing taxable temporary differences; (ii) future taxable income exclusive of reversing temporary difference and carryforwards; (iii) taxable income in prior carryback years if carryback is permitted under applicable tax law; and (iv) tax planning strategies. The Company's net deferred income tax asset is not more likely than not to be utilized due to the lack of sufficient sources of future taxable income and cumulative book losses which have resulted over the years.

As of December 31, 2018, the Company has U.S. federal and state net operating loss (NOL) carryforwards of approximately $415.6 million. Of these NOLs, $237.8 million will expire in various years beginning in 2025 through 2037. $177.8 million of NOLs were generated post December 31, 2017 and carryforward indefinitely. In addition, the Company has U.S. federal tax credits of $52.3 million which will expire in various years beginning in 2022 through 2038.

The use of the Company's U.S. federal NOL and tax credit carryforwards in future years are restricted due to changes in the Company's ownership and tax attributes acquired through the Company's acquisitions. As of December 31, 2018, $13.5 million of the Company's U.S. Federal NOLs are limited for use over the years 2019 – 2028 in which a range of such amounts could be utilized on an annual basis of $0.2 million to $1.4 million. The remaining $402.1 million of NOLs is not limited and can be offset against future taxable income, subject to certain limitations for newly enacted tax legislation. The Company adopted ASU 2016-09 as of January 1, 2017. Accordingly, the Company recognized the previously unrecognized excess tax benefits of approximately $18.6 million ($6.5 million tax effected) recorded as deferred tax assets with a corresponding offsetting full valuation allowance at the beginning of 2017 without any tax impact.

The reconciliation of the reported estimated income tax benefit to the amount that would result by applying the U.S. federal statutory tax rate to the net income is as follows (in thousands):


	Year Ended December 31,
	2018		2017		2016

United States federal tax at statutory rate	$	(36,005)	$	(6,869)	$	(20,489)
State taxes (net of federal benefit)	(11,133)		(735)		(3,116)
Deferred income tax adjustments	(4,435)		607		173
Deferred state blended rate adjustments	—		(485)		(32)
Deferred federal rate change reduction in corporate rate	—		39,447		—
Research credit, net	(8,466)		(8,455)		(2,551)
Orphan drug credit, net	(872)		(1,853)		(571)
Other permanent items	148		276		145
Equity-based compensation	758		2,067		1,997
Change in valuation allowance	60,005		(24,000)		24,444
Income tax expense/(benefit)	$	—	$	—	$	—

A reconciliation of the beginning and ending amount of gross unrecognized tax benefits is as follows (in thousands):


	Year Ended December 31,
	2018		2017		2016
Beginning balance	$	3,395	$	2,465	$	2,425
Increases for current year tax positions	642		569		308
Increases/(decreases) for prior year tax positions	281		361		(268)
Ending balance	$	4,318	$	3,395	$	2,465

As of December 31, 2018 and 2017, of the total gross unrecognized tax benefits, approximately $4.5 million and $3.4 million would favorably impact the Company's effective income tax rate, respectively. Although, due to the Company's determination that the deferred income tax asset would not more likely than not be realized, a valuation allowance would be recorded, therefore, zero net impact would result within the Company's effective income tax rate. The Company's uncertain income tax position liability has been recorded to deferred income taxes to offset the tax attribute carryforward amounts.

For the years ended December 31, 2018, 2017 and 2016, the Company has not recognized any interest or penalties related to the uncertain income tax positions due to the fact such position is related to tax attribute carryforwards which have not yet been utilized. The Company does not expect its unrecognized income tax position to significantly decrease within the next twelve months.

The Company's U.S. Federal and state income tax returns from 2001 forward remain open to examination due to the carryover of unused net operating losses and tax credits.

As more fully described in Note 2 to the consolidated financial statements, the Tax Act was signed into law making significant changes to the Internal Revenue Code on December 22, 2017. Under ASC 740, the effects of the new legislation are to be recognized in the period of enactment. As such, recognition of the tax impact of the Tax Act was required in the interim and annual periods that include December 22, 2017. As a result, the Company revalued the deferred tax asset as of December 31, 2017, fully offset by a valuation allowance without impact to the financial statements.

Collaboration and Other Agreements	12 Months Ended
Collaboration and Other Agreements	Dec. 31, 2018
Collaboration and License Agreements [Abstract]
Collaboration and Other Agreements	Collaboration and Other Agreements Incyte In October 2017, the Company entered into an exclusive global collaboration and license agreement with Incyte for MGA012 (also known as INCMGA0012), an investigational monoclonal antibody that inhibits programmed cell death protein 1 (PD-1) (Incyte Agreement). Incyte has obtained exclusive worldwide rights for the development and commercialization of MGA012 in all indications, while the Company retains the right to develop its pipeline assets in combination with MGA012. The Company received a $150.0 million upfront payment from Incyte when the transaction closed in the fourth quarter of 2017. Under the terms of the Incyte Agreement, Incyte will lead global development of MGA012. Assuming successful development and commercialization by Incyte, the Company could receive up to approximately $420.0 million in development and regulatory milestones, and up to $330.0 million in commercial milestones. As of December 31, 2018, the Company has recognized $15.0 million in development milestones under this agreement. If commercialized, the Company would be eligible to receive tiered royalties of 15% to 24% on any global net sales. The Company retains the right to develop its pipeline assets in combination with MGA012, with Incyte commercializing MGA012 and the Company commercializing its asset(s), if any such potential combinations are approved. In addition, the Company retains the right to manufacture a portion of both companies' global commercial supply needs of MGA012, subject to a separate commercial supply agreement. Finally, Incyte funded the Company's activities related to the ongoing monotherapy clinical study and will continue to fund certain related clinical activities. Upon the adoption of ASC 606, the Company evaluated the Incyte Agreement under the provisions of ASC 606 and identified the following two performance obligations under the agreement: (i) the license of MGA012 and (ii) the performance of certain clinical activities through a brief technology transfer period. The Company determined that the license and clinical activities are separate performance obligations because they are capable of being distinct, and are distinct in the context of the contract. The license has standalone functionality as it is sublicensable, Incyte has significant capabilities in performing clinical trials, and Incyte is capable of performing these activities without the Company's involvement; the Company performed the activities during the transfer period as a matter of convenience. The Company determined that the transaction price of the Incyte Agreement at inception was $154.0 million, consisting of the consideration to which the Company was entitled in exchange for the license and an estimate of the consideration for clinical activities to be performed. The transaction price was allocated to each performance obligation based on their relative standalone selling price. The standalone selling price of the license was determined using the adjusted market assessment approach considering similar collaboration and license agreements. The standalone selling price for agreed-upon clinical activities to be performed was determined using the expected cost approach based on similar arrangements the Company has with other parties. The potential development and regulatory milestone payments are fully constrained until the Company concludes that achievement of the milestone is probable and that recognition of revenue related to the milestone will not result in a significant reversal in amounts recognized in future periods, and as such have been excluded from the transaction price. Any consideration related to sales-based milestones and royalties will be recognized when the related sales occur, as they were determined to relate predominantly to the license granted to Incyte and, therefore, have also been excluded from the transaction price. The Company re-assesses the transaction price in each reporting period and when events whose outcomes are resolved or other changes in circumstances occur. During the year ended December 31, 2018, it became probable that a significant reversal of cumulative revenue would not occur for three development milestones totaling $15.0 million related to MGA012 meeting certain clinical proof-of-concept criteria. Therefore the associated consideration was added to the estimated transaction price and was recognized as revenue. The Company recognized the $150.0 million allocated to the license when it satisfied its performance obligation and transferred the license to Incyte in December 2017. The $4.0 million allocated to the clinical activities was recognized over the period from the effective date of the agreement until such time as the clinical activities were transferred to Incyte using an input method according to research and development costs incurred to date compared to estimated total research and development costs. These clinical activities were substantially completed as of June 30, 2018. Prior to the adoption of ASC 606 on January 1, 2018, the accounting for this agreement did not materially differ from the accounting under ASC 606. The Company recognized revenue of $18.8 million and $151.1 million under the Incyte Agreement during the years ended December 31, 2018 and 2017, respectively. The revenue recognized during the year ended December 31, 2018 included milestone revenue of $15.0 million. The Company also has an agreement with Incyte, which was signed in 2018, under which the Company is to perform development and manufacturing services for Incyte’s clinical needs of MGA012. The Company evaluated this agreement under ASC 606 and identified one performance obligation under the agreement - to perform services related to manufacturing the clinical supply of MGA012. The transaction price is based on the costs incurred to develop and manufacture drug product and drug substance, and is recognized over time as the services are provided, as the performance by the Company does not create an asset with an alternative use and the Company has an enforceable right to payment for the performance completed to date. During the year ended December 31, 2018, the Company recognized revenue of $22.2 million for services performed under this agreement. Servier In September 2012, the Company entered into a collaboration agreement with Servier and granted it exclusive options to obtain three separate exclusive licenses to develop and commercialize DART molecules, consisting of those designated by the Company as flotetuzumab (also known as MGD006 or S80880) and MGD007, as well as a third DART molecule, in all countries other than the United States, Canada, Mexico, Japan, South Korea and India (Servier Agreement). During 2014, Servier exercised its exclusive option to develop and commercialize flotetuzumab. During 2016 Servier notified the Company that it did not intend to exercise the option for the third DART molecule, and in November 2018, Servier notified the Company that it did not intend to exercise the option for MGD007. Upon execution of the agreement, Servier made a nonrefundable payment of $20.0 million to the Company. In addition, if Servier successfully develops, obtains regulatory approval for, and commercializes flotetuzumab, the Company will be eligible to receive up to $22.5 million in clinical milestone payments, $76.0 million in regulatory milestone payments and $210.0 million in sales milestone payments. In addition to these milestones, the Company and Servier will share Phase 2 and Phase 3 development costs. Under this agreement, Servier would be obligated to pay the Company from low double-digit to mid-teen royalties on net product sales in its territories. Upon the adoption of ASC 606, the Company evaluated the Servier Agreement under the provisions of ASC 606 and concluded that Servier is a customer prior to the exercise of any of the three options. The Company identified the following material promises under the arrangement for each of the three molecules: (i) a limited evaluation license to conduct activities under the research plan and (ii) research and development services concluding with an option trigger data package. The Servier Agreement also provided exclusive options for an exclusive license to research, develop, manufacture and commercialize each subject molecule. The Company evaluated these options and concluded that the options were not issued at a significant and incremental discount, and therefore do not provide material rights. As such, they are excluded as performance obligations at the outset of the arrangement. The Company determined that each license and the related research and development services were not distinct from one another, as the license has limited value without the performance of the research and development activities. As such, the Company determined that these promises should be combined into a single performance obligation for each molecule, resulting in a total of three performance obligations; one for flotetuzumab, one for MGD007, and one for the third DART molecule. The Company determined that the $20.0 million upfront payment from Servier constituted the entirety of the consideration to be included in the transaction price as of the outset of the arrangement, and the transaction price was allocated to the three performance obligations based on their relative standalone selling price. The milestone payments that the Company was eligible to receive prior to the exercise of the options were excluded from the transaction price, as all milestone amounts were fully constrained based on the probability of achievement. Two milestones were achieved in 2014 when the INDs for flotetuzumab and MGD007 were cleared by the Food and Drug Administration (FDA). Upon achievement of each milestone, the constraint related to the $5.0 million milestone payment was removed and the transaction price was re-assessed. This variable consideration was allocated to each specific performance obligation in accordance with ASC 606. Revenue associated with each performance obligation is being recognized as the research and development services are provided using an input method according to research and development costs incurred to date compared to estimated total research and development costs. The transfer of control occurs over this time period and, in management’s judgment, is the best measure of progress towards satisfying the performance obligation. The full transaction price allocated to flotetuzumab and the third DART molecule was recognized as revenue prior to the adoption of ASC 606 on January 1, 2018 as the option periods had ended. The development period for MGD007 was estimated to be 75 months, ending in December 2018, therefore the transaction price allocated to MGD007 was being recognized through that date. When Servier notified the Company that it was not exercising the option for MGD007 in November 2018, the Company recognized the remaining deferred revenue related to MGD007. Upon the adoption of ASC 606 on January 1, 2018, the pattern of revenue recognition for the upfront fee and the accounting for the milestones received in 2014 changed, but there was no material impact to revenue recognized during the year ended December 31, 2018. During the years ended December 31, 2018, 2017 and 2016 the Company recognized revenue of $1.9 million, $1.1 million and $1.1 million, respectively, related to the MGD007 option. At December 31, 2018, no revenue related to the MGD007 option was deferred. The deferred revenue balance related to the MGD007 option as of December 31, 2017, prior to the adoption of ASC 606, was $1.1 million, all of which was current. As discussed above, in 2014, Servier exercised its option to obtain a license to develop and commercialize flotetuzumab in its territories and paid the Company a $15.0 million license grant fee. Upon exercise, the Company's contractual obligations include (i) granting Servier an exclusive license to its intellectual property, (ii) technical, scientific and intellectual property support to the research plan and (iii) participation on an executive committee and a research and development committee. Under the terms of the Servier Agreement, the Company and Servier will share costs incurred to develop flotetuzumab during the license term. Due to the fact that both parties share costs and are exposed to significant risks and rewards dependent on the commercial success of the product, the Company determined that the arrangement is a collaborative arrangement within the scope of ASC 808. The arrangement consists of two components; the license of flotetuzumab and the research and development activities, including committee participation, to support the research plan. Under the provisions of ASC 808, the Company has determined that it will use ASC 606 by analogy to recognize the revenue related to the license. The Company evaluated its performance obligation to provide Servier with an exclusive license to develop and commercialize flotetuzumab and determined that its transaction price is equal to the license grant fee payment of $15.0 million and Servier consumes the benefits of the license over time as the research and development activities are performed. Therefore, the Company will recognize the transaction price over the development period, using an input method according to research and development costs incurred to date compared to estimated total research and development costs. The additional potential clinical, regulatory and sales milestones are fully constrained and have been excluded from the transaction price. Prior to the adoption of ASC 606 on January 1, 2018, the Company recognized the license grant fee over the expected period of development on a straight-line basis. The deferred revenue balance related to the flotetuzumab license grant fee as of December 31, 2017, prior to the adoption of ASC 606, was $7.4 million. The adoption of ASC 606 increased that balance by approximately $6.4 million. The adoption of ASC 606 increased revenue recognized during the year ended December 31, 2018 by $0.1 million, and it will increase the revenue to be recognized in the future as the pattern of revenue recognition has changed. During the years ended December 31, 2018, 2017 and 2016 the Company recognized revenue of $1.2 million, $1.4 million, and $2.2 million, respectively, related to the flotetuzumab license grant fee. At December 31, 2018, $12.6 million of revenue related to the flotetuzumab license grant fee was deferred, $0.9 million of which was current and $11.7 million of which was non-current. The research and development activities component of the arrangement is not analogous to ASC 606, therefore the Company will follow its policy to record expense incurred as research and development expense and reimbursements received from Servier will be recognized as an offset to research and development expense on the consolidated statement of operations and comprehensive loss during the development period. During the three years ended December 31, 2018, 2017 and 2016 the Company recorded approximately $6.0 million, $3.2 million and $2.6 million, respectively, as an offset to research and development expense under this collaborative arrangement. Zai Lab In November 2018, the Company entered into a collaboration and license agreement with Zai Lab (Zai Lab Agreement) under which Zai Lab obtained regional development and commercialization rights in mainland China, Hong Kong, Macau and Taiwan for (i) margetuximab, an immune-optimized anti-HER2 monoclonal antibody, (ii) MGD013, a bispecific DART molecule designed to provide coordinate blockade of PD-1 and LAG-3 for the potential treatment of a range of solid tumors and hematological malignancies, and (iii) an undisclosed multi-specific TRIDENT molecule in preclinical development. Zai Lab will lead clinical development of these molecules in its territory. Under the terms of the Zai Lab Agreement, Zai Lab paid the Company an upfront payment of $25.0 million, less foreign withholding tax of $2.50 million, which was received in January 2019. Assuming successful development and commercialization of margetuximab, MGD013 and the TRIDENT molecule, the Company could receive up to $140.0 million in development and regulatory milestones. In addition, Zai Lab would pay the Company double-digit royalties on annual net sales of the assets, which may be subject to adjustment in specified circumstances. The Company evaluated the Zai Lab Agreement under the provisions of ASC 606 and identified the following material promises under the arrangement for each of the two product candidates, margetuximab and MGD013: (i) an exclusive license to develop and commercialize the product candidate in Zai Lab’s territory and (ii) certain research and development activities. The Company determined that each license and the related research and development activities were not distinct from one another, as the license has limited value without the performance of the research and development activities. As such, the Company determined that these promises should be combined into a single performance obligation for each product candidate. Activities related to margetuximab and MGD013 are separate performance obligations from each other because they are capable of being distinct, and are distinct in the context of the contract. The Company evaluated the promises related to the TRIDENT molecule and determined they were immaterial in context of the contract, therefore there is no performance obligation related to that molecule. The Company determined that the $25.0 million (less foreign withholding tax of $2.5 million) upfront payment from Zai Lab constituted the entirety of the consideration to be included in the transaction price as of the outset of the arrangement, and the transaction price was allocated to the two performance obligations based on their relative standalone selling price. The standalone selling price of the performance obligations was determined using the adjusted market assessment approach considering similar collaboration and license agreements. The potential development and regulatory milestone payments are fully constrained until the Company concludes that achievement of the milestone is probable, and that recognition of revenue related to the milestone will not result in a significant reversal in amounts recognized in future periods, and as such have been excluded from the transaction price. Any consideration related to royalties will be recognized when the related sales occur, as they were determined to relate predominantly to the license granted to Zai Lab and, therefore, have also been excluded from the transaction price. The Company re-assesses the transaction price in each reporting period and when events whose outcomes are resolved or other changes in circumstances occur. Due to the relatively short-term nature of the recognition period, the revenue associated with the MGD013 performance obligation is being recognized on a straight-line basis as the Company performs research and development activities under the agreement. The fixed consideration related to the margetuximab performance obligation is also being recognized on a straight-line basis as the Company performs research and development activities under the agreement. Straight-line recognition is materially consistent with the pattern of performance of the research and development activities of each product candidate. The variable consideration related to the margetuximab performance obligation will be recognized upon certain regulatory achievements. During the year ended December 31, 2018, the Company recognized revenue of $1.3 million related to the Zai Lab Agreement. At December 31, 2018, $21.1 million of revenue was deferred under this agreement, $16.1 million of which was current. Roche In December 2017, the Company entered into a research collaboration and license agreement with Roche to jointly discover and develop novel bispecific molecules to undisclosed targets (Roche Agreement). During the research term, both companies will leverage their respective platforms, including the Company's DART platform and Roche's CrossMAb and DutaFab technologies to select a bispecific format and lead product candidate. Roche would then further develop and commercialize any such product candidate. Each company will be responsible for their own expenses during the research period. Under the terms of the Roche Agreement, Roche received rights to use certain of the Company’s intellectual property rights to exploit collaboration compounds and products, and paid the Company an upfront payment of $10.0 million which was received in January 2018. The Company will also be eligible to receive up to $370.0 million in potential milestone payments and royalties on future sales. As of December 31, 2018, the Company has not recognized any milestone revenue under this agreement. Upon the adoption of ASC 606, the Company evaluated the Roche Agreement under the provisions of ASC 606 and identified the following promises under the agreement: (i) the non-exclusive, non-transferable, non-sublicensable license to the Company's intellectual property and (ii) the performance of certain activities during the research period. The Company determined that the license is capable of being distinct, but is not distinct in the context of the contract because it has limited value to Roche without the research activities required to be performed by the Company. Therefore, the Company concluded that there is one performance obligation under the agreement. The Company determined that the transaction price of the Roche Agreement was $10.0 million. The potential milestone payments are fully constrained and have been excluded from the transaction price. Any consideration related to sales-based royalties will be recognized when the related sales occur as they were determined to relate predominantly to the license granted to Roche and therefore have also been excluded from the transaction price. The $10.0 million transaction price is being recognized over the expected research period, which is 30 months, using a cost-based input method to measure performance. Prior to the adoption of ASC 606 on January 1, 2018, the accounting for this agreement did not materially differ from the accounting under ASC 606. The Company recognized revenue under this agreement of $4.0 million during the year ended December 31, 2018. At December 31, 2018, $6.0 million of revenue was deferred under this agreement, $4.0 million of which was current and $2.0 million of which was non-current. At December 31, 2017, $10.0 million of revenue was deferred under this agreement, $4.0 million of which was current and $6.0 million of which was non-current. Provention In May 2018, the Company entered into a license agreement with Provention pursuant to which the Company granted Provention exclusive global rights for the purpose of developing and commercializing MGD010 (renamed PRV-3279), a CD32B x CD79B DART molecule being developed for the treatment of autoimmune indications (Provention License Agreement). As partial consideration for the Provention License Agreement, Provention granted the Company a warrant to purchase shares of Provention’s common stock at an exercise price of $2.50 per share. The warrant expires on May 7, 2025. If Provention successfully develops, obtains regulatory approval for, and commercializes PRV-3279, the Company will be eligible to receive up to $65.0 million in development and regulatory milestones and up to $225.0 million in commercial milestones. As of December 31, 2018, the Company has not recognized any milestone revenue under this agreement. If commercialized, the Company would be eligible to receive single-digit royalties on net sales of the product. The license agreement may be terminated by either party upon a material breach or bankruptcy of the other party, by Provention without cause upon prior notice to the Company, and by the Company in the event that Provention challenges the validity of any licensed patent under the agreement, but only with respect to the challenged patent. Also in May 2018, the Company entered into an asset purchase agreement with Provention pursuant to which Provention acquired the Company’s interest in teplizumab (renamed PRV-031), a monoclonal antibody being developed for the treatment of type 1 diabetes (Asset Purchase Agreement). As partial consideration for the Asset Purchase Agreement, Provention granted the Company a warrant to purchase shares of Provention’s common stock at an exercise price of $2.50 per share. The warrant expires on May 7, 2025. If Provention successfully develops, obtains regulatory approval for, and commercializes PRV-031, the Company will be eligible to receive up to $170.0 million in regulatory milestones and up to $225.0 million in commercial milestones. If commercialized, the Company would be eligible to receive single-digit royalties on net sales of the product. Provention has also agreed to pay third-party obligations, including low single-digit royalties, a portion of which is creditable against royalties payable to the Company, aggregate milestone payments of up to approximately $1.3 million and other consideration, for certain third-party intellectual property under agreements Provention is assuming pursuant to the Asset Purchase Agreement. Further, Provention is required to pay the Company a low double-digit percentage of certain consideration to the extent it is received in connection with a future grant of rights to PRV-031 by Provention to a third party. The Company evaluated the Provention License Agreement and Asset Purchase Agreement under the provisions of ASC 606 and determined that they should be accounted for as a single contract and identified two performance obligations within that contract: (i) the license of MGD010 and (ii) the title to teplizumab. The Company determined that the transaction price of the Provention agreements was $6.1 million, based on the Black-Scholes valuation of the warrants to purchase a total of 2,432,688 shares of Provention's common stock. The transaction price was allocated to each performance obligation based on the number of shares of common stock the Company is entitled to purchase under each warrant. The potential development and regulatory milestone payments are fully constrained until the Company concludes that achievement of the milestone is probable and that recognition of revenue related to the milestone will not result in a significant reversal in amounts recognized in future periods, and as such have been excluded from the transaction price. Any consideration related to sales-based milestones and royalties will be recognized when the related sales occur, therefore they have also been excluded from the transaction price. The Company re-assesses the transaction price in each reporting period and when events whose outcomes are resolved or other changes in circumstances occur. The Company recognized revenue of $6.1 million when it satisfied its performance obligations and transferred the MGD010 license and teplizumab assets to Provention in May 2018. The warrants are reported in other assets on the balance sheet at December 31, 2018 and will be revalued at each reporting period until exercised or the warrants lapse. The Company revalued the warrants based on current Black-Scholes parameters as of December 31, 2018, and recorded a decrease of $4.2 million in other assets. This revaluation is reflected in other income (expense) on the consolidated statements of operations and comprehensive loss for the year ended December 31, 2018. Janssen In December 2014, the Company entered into a collaboration and license agreement with Janssen for the development and commercialization of MGD011 (also known as JNJ-64052781 or duvortuxizumab), a product candidate that incorporates the Company's proprietary DART technology to simultaneously target CD19 and CD3 for the potential treatment of B-cell hematological malignancies (MGD011 Agreement). The Company contemporaneously entered into an agreement with JJDC under which JJDC agreed to purchase 1,923,077 new shares of the Company's common stock for proceeds of $75.0 million. Upon closing the transaction in January 2015, the Company received a $50.0 million upfront payment from Janssen as well as the $75.0 million investment in the Company's common stock. In August 2017, Janssen notified the Company that they were terminating the MGD011 Agreement. No revenue was recognized under the MGD011 Agreement during the years ended December 31, 2017 and 2018. The Company recognized revenue of $2.0 million during the year ended December 31, 2016. In May 2016, the Company entered into a collaboration and license agreement with Janssen, a related party through ownership of the Company's common stock, for the development and commercialization of MGD015, a product candidate that incorporates the Company's proprietary DART technology to simultaneously target CD3 and an undisclosed tumor target for the potential treatment of various hematological malignancies and solid tumors (MGD015 Agreement). Under the MGD015 Agreement, the Company granted an exclusive license to Janssen to develop and commercialize MGD015. The Company received a $75.0 million upfront payment from Janssen upon closing the transaction, which was recognized as revenue in 2016. In January 2018, Janssen notified the Company that they were terminating the MGD015 Agreement. No revenue was recognized under the MGD015 Agreement during the year ended December 31, 2018. The Company recognized revenue of $0.6 million and $75.8 million during the years ended December 31, 2017 and 2016, respectively. The revenue under both the MGD011 and MGD015 Agreements was fully recognized prior to the adoption of ASC 606. NIAID Contract The Company entered into a contract with the National Institute of Allergy and Infectious Diseases (NIAID), effective as of September 15, 2015, to perform product development and to advance up to two DART molecules, including MGD014. Under this contract, the Company will develop these product candidates for Phase 1/2 clinical trials as therapeutic agents, in combination with latency reversing treatments, to deplete cells infected with human immunodeficiency virus (HIV) infection. NIAID does not receive goods or services from the Company under this contract, therefore the Company does not consider NIAID to be a customer and concluded this contract is outside the scope of ASC 606. This contract includes a base period of $7.5 million to support development of MGD014 through IND application submission with the FDA, as well as up to $17.0 million in additional development funding via NIAID options. Should NIAID fully exercise such options, the Company could receive total payments of up to $24.5 million. The total potential period of performance under the award is from September 15, 2015 through September 14, 2022. During the year ended December 31, 2017, NIAID exercised the first option in the amount of $10.8 million. The Company recognized revenue of $1.3 million, $1.7 million and $5.1 million under this contract during the years ended December 31, 2018, 2017 and 2016, respectively.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Operating Leases

The Company leases manufacturing, office and laboratory space in Rockville, Maryland under five leases that have terms that expire between 2019 and 2027 unless renewed. During the year ended December 31, 2017, the Company entered into an agreement to sublease a portion of the space it leases. As of December 31, 2018, the Company will receive $1.1 million in future payments under this sublease. The Company also leases office and laboratory space in Brisbane, California under a lease that expires in November 2023.

The Rockville leases include a lease executed in July 2015 for space that the Company uses as its headquarters with office, laboratory, and manufacturing space. Under the terms of the lease, which commenced on January 1, 2016, the Company received an assignment fee from the former tenant and a tenant improvement allowance from the landlord totaling $5.1 million. During 2017, the Company executed a lease amendment for its headquarters building which extends the term of the lease to August 2027, restructures the rent due under the lease, and provides for an additional tenant improvement allowance from the landlord of $7.5 million. The assignment fee and tenant improvement allowances have been recorded as deferred rent and are being recognized over the new lease term.

All of the leases contain rent escalation clauses and certain leases contain rent abatements. For financial reporting purposes, rent expense is charged to operations on a straight-line basis over the term of the lease. As of December 31, 2018 and 2017, the Company had recorded a deferred rent liability of $11.3 million and $12.3 million, respectively. Rent expense for the years ended December 31, 2018, 2017 and 2016 was $4.4 million, $3.1 million and $3.0 million, respectively.

Future minimum lease payments under noncancelable operating leases as of December 31, 2018 are as follows (in thousands):


2019	$	6,323
2020	4,757
2021	4,724
2022	4,865
2023	4,680
Thereafter	13,786
	$	39,135

Contingencies

From time to time, the Company may be subject to various litigation and related matters arising in the ordinary course of business. The Company does not believe it is currently subject to any material matters where there is at least a reasonable possibility that a material loss may be incurred.

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation The consolidated financial statements include the accounts of MacroGenics, Inc. and its wholly owned subsidiary, MacroGenics UK Limited. All intercompany accounts and transactions have been eliminated in consolidation. The Company currently operates in one operating segment. Operating segments are defined as components of an enterprise about which separate discrete information is available for the chief operating decision maker, or decision making group, in deciding how to allocate resources and assessing performance. The Company views its operations and manages its business in one segment, which is developing monoclonal antibody-based therapeutics for cancer, autoimmune and infectious diseases.
Use of Estimates	Use of Estimates The preparation of the financial statements in accordance with generally accepted accounting principles (GAAP) requires the Company to make estimates and judgments in certain circumstances that affect the reported amounts of assets, liabilities, revenues and expenses, and related disclosure of contingent assets and liabilities. In preparing these consolidated financial statements, management has made its best estimates and judgments of certain amounts included in the financial statements, giving due consideration to materiality. On an ongoing basis, the Company evaluates its estimates, including those related to revenue recognition, fair values of assets, stock-based compensation, income taxes, preclinical study and clinical trial accruals and other contingencies. Management bases its estimates on historical experience or on various other assumptions that it believes to be reasonable under the circumstances. Actual results could differ from these estimates.
Cash, Cash Equivalents and Marketable Securities	Cash, Cash Equivalents and Marketable Securities The Company considers all investments in highly liquid financial instruments with a maturity of 90 days or less at the date of purchase to be cash equivalents. Cash and cash equivalents includes investments in money market funds with commercial banks and financial institutions, securities issued by the U.S. government and its agencies, Government Sponsored Enterprise agency debt obligations and corporate debt obligations. Cash equivalents are stated at amortized cost, plus accrued interest, which approximates fair value. The Company carries marketable securities classified as available-for-sale at fair value as determined by prices for identical or similar securities at the balance sheet date. Marketable securities consist of Level 2 financial instruments in the fair-value hierarchy. The Company records unrealized gains and losses as a component of other comprehensive loss within the statements of operations and comprehensive loss and as a separate component of stockholders' equity. Realized gains or losses on available-for-sale securities are determined using the specific identification method and the Company includes net realized gains and losses in other income (expense). At each balance sheet date, the Company assesses available-for-sale securities in an unrealized loss position to determine whether the unrealized loss is other-than-temporary. The Company considers factors including: the significance of the decline in value compared to the cost basis, underlying factors contributing to a decline in the prices of securities in a single asset class, the length of time the market value of the security has been less than its cost basis, the security's relative performance versus its peers, sector or asset class, expected market volatility and the market and economy in general. The Company also evaluates whether it is more likely than not that it will be required to sell a security prior to recovery of its fair value. An impairment loss is recognized at the time the Company determines that a decline in the fair value below its cost basis is other-than-temporary. There were no unrealized losses at December 31, 2018 or 2017 that the Company determined to be other-than-temporary.
Accounts Receivable	Accounts Receivable Accounts receivable that management has the intent and ability to collect are reported in the consolidated balance sheets at outstanding amounts, less an allowance for doubtful accounts. The Company writes off uncollectible receivables when the likelihood of collection is remote. The Company evaluates the collectability of accounts receivable on a regular basis. The allowance, if any, is based upon various factors including the financial condition and payment history of customers, an overall review of collections experience on other accounts and economic factors or events expected to affect future collections experience. No allowance was recorded as of December 31, 2018 or 2017, as the Company has a history of collecting on all outstanding accounts.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company's financial instruments consist of cash and cash equivalents, marketable securities, accounts receivable, accounts payable and accrued expenses. The carrying amount of accounts receivable, accounts payable and accrued expenses are generally considered to be representative of their respective fair values because of their short-term nature. The Company accounts for recurring and non-recurring fair value measurements in accordance with the Financial Accounting Standards Board (FASB) Accounting Standards Codification (ASC) 820, Fair Value Measurements and Disclosures (ASC 820). ASC 820 defines fair value, establishes a fair value hierarchy for assets and liabilities measured at fair value, and requires expanded disclosures about fair value measurements. The ASC 820 hierarchy ranks the quality of reliability of inputs, or assumptions, used in the determination of fair value and requires assets and liabilities carried at fair value to be classified and disclosed in one of the following three categories: •Level 1 – Fair value is determined by using unadjusted quoted prices that are available in active markets for identical assets and liabilities. •Level 2 – Fair value is determined by using inputs other than Level 1 quoted prices that are directly or indirectly observable. Inputs can include quoted prices for similar assets and liabilities in active markets or quoted prices for identical assets and liabilities in inactive markets. Related inputs can also include those used in valuation or other pricing models, such as interest rates and yield curves that can be corroborated by observable market data. •Level 3 – Fair value is determined by inputs that are unobservable and not corroborated by market data. Use of these inputs involves significant and subjective judgments to be made by a reporting entity – e.g., determining an appropriate adjustment to a discount factor for illiquidity associated with a given security. The Company evaluates financial assets and liabilities subject to fair value measurements on a recurring basis to determine the appropriate level at which to classify them each reporting period. This determination requires the Company to make subjective judgments as to the significance of inputs used in determining fair value and where such inputs lie within the ASC 820 hierarchy.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash, cash equivalents, marketable securities and accounts receivable. The Company maintains its cash and money market funds with financial institutions that are federally insured. While balances deposited in these institutions often exceed Federal Deposit Insurance Corporation limits, the Company has not experienced any losses on related accounts to date. The Company's investment policy limits investments to certain types of debt securities issued by the U.S. government, its agencies and institutions with investment-grade credit ratings and places restrictions on maturities and concentration by type and issuer. The counterparties are various corporations, financial institutions and government agencies of high credit standing.
Property, Equipment and Software	Property, Equipment and SoftwareProperty, equipment and software are stated at cost. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation or amortization are removed from the accounts and any resulting gain or loss is credited or charged to operations. Repairs and maintenance costs are expensed as incurred.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company assesses the recoverability of its long-lived assets in accordance with the provisions of ASC 360, Property, Plant and Equipment. ASC 360 requires that long-lived assets be reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of the long-lived asset is measured by a comparison of the carrying amount of the asset to future undiscounted net cash flows expected to be generated by the asset or asset group. If carrying value exceeds the sum of undiscounted cash flows, the Company then determines the fair value of the underlying asset group. Any impairment to be recognized is measured by the amount by which the carrying amount of the asset group exceeds the estimated fair value of the asset group. Assets to be disposed of are reported at the lower of the carrying amount or fair value, less costs to sell. For the years ended December 31, 2018, 2017 and 2016, the Company determined that there were no impaired assets.
Income Taxes	Income Taxes Deferred tax assets and liabilities are determined based on differences between the financial reporting and tax basis of assets and liabilities and are measured using the enacted tax rates and laws that are expected to be in effect when the differences are expected to reverse. The effect on deferred tax assets and liabilities of a change in tax rates is recognized as income in the period that such tax rate changes are enacted. The measurement of a deferred tax asset is reduced, if necessary, by a valuation allowance if it is more likely than not that some portion or all of the deferred tax asset will not be realized. Financial statement recognition of a tax position taken or expected to be taken in a tax return is determined based on a more-likely-than-not threshold of that position being sustained. If the tax position meets this threshold, the benefit to be recognized is measured as the largest amount that is more likely than not to be realized upon ultimate settlement. The Company's policy is to record interest and penalties related to uncertain tax positions as a component of income tax expense.
Revenues	Revenues Beginning on January 1, 2018, the Company recognizes revenue under Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers and all related amendments (collectively ASC 606) when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. The Company enters into licensing agreements that are within the scope of ASC 606, under which it may license rights to research, develop, manufacture and commercialize its product candidates to third parties. The terms of these arrangements typically include payment to the Company of one or more of the following: non-refundable, upfront license fees; reimbursement of certain costs; customer option exercise fees; development, regulatory and commercial milestone payments; and royalties on net sales of licensed products. The Company may also enter into development and manufacturing service agreements with its collaborators. For each arrangement that results in revenues, the Company identifies all performance obligations, which may include a license to intellectual property and know-how, research and development activities, transition activities and/or manufacturing services. In order to determine the transaction price, in addition to any upfront payment, the Company estimates the amount of variable consideration at the outset of the contract either utilizing the expected value or most likely amount method, depending on the facts and circumstances relative to the contract. The Company constrains (reduces) the estimates of variable consideration such that it is probable that a significant reversal of previously recognized revenue will not occur. When determining if variable consideration should be constrained, management considers whether there are factors outside the Company’s control that could result in a significant reversal of revenue. In making these assessments, the Company considers the likelihood and magnitude of a potential reversal of revenue. These estimates are re-assessed each reporting period as required. Once the estimated transaction price is established, amounts are allocated to the performance obligations that have been identified. The transaction price is generally allocated to each separate performance obligation on a relative standalone selling price basis. The Company must develop assumptions that require judgment to determine the standalone selling price in order to account for these agreements. To determine the standalone selling price, the Company’s assumptions may include (i) the probability of obtaining marketing approval for the product candidate, (ii) estimates regarding the timing and the expected costs to develop and commercialize the product candidate, and (iii) estimates of future cash flows from potential product sales with respect to the product candidate. Standalone selling prices used to perform the initial allocation are not updated after contract inception. The Company does not include a financing component to its estimated transaction price at contract inception unless it estimates that certain performance obligations will not be satisfied within one year. Amounts received prior to revenue recognition are recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current portion of deferred revenue in the accompanying consolidated balance sheets. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion. Licenses. If the license to the Company’s intellectual property is determined to be distinct from the other promises or performance obligations identified in the arrangement, the Company recognizes revenue from non-refundable, upfront fees allocated to the license when the license is transferred to the customer and when (or as) the customer is able to use and benefit from the license. In assessing whether a promise or performance obligation is distinct from the other promises, the Company considers factors such as the research, development, manufacturing and commercialization capabilities of the licensee and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the licensee can benefit from a promise for its intended purpose without the receipt of the remaining promise, whether the value of the promise is dependent on the unsatisfied promise, whether there are other vendors that could provide the remaining promise, and whether it is separately identifiable from the remaining promise. For licenses that are combined with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The measure of progress, and thereby periods over which revenue should be recognized, are subject to estimates by management and may change over the course of the research and development and licensing agreement. Such a change could have a material impact on the amount of revenue the Company records in future periods. Research, Development and/or Manufacturing Services. The promises under the Company’s agreements may include research and development or manufacturing services to be performed by the Company on behalf of the counterparty. If these services are determined to be distinct from the other promises or performance obligations identified in the arrangement, the Company recognizes the transaction price allocated to these services as revenue over time based on an appropriate measure of progress when the performance by the Company does not create an asset with an alternative use and the Company has an enforceable right to payment for the performance completed to date. If these services are determined not to be distinct from the other promises or performance obligations identified in the arrangement, the Company recognizes the transaction price allocated to the combined performance obligation as the related performance obligations are satisfied. Customer Options. If an arrangement contains customer options, the Company evaluates whether the options are material rights because they allow the customer to acquire additional goods or services for free or at a discount. If the customer options are determined to represent a material right, the material right is recognized as a separate performance obligation at the outset of the arrangement. The Company allocates the transaction price to material rights based on the relative standalone selling price, which is determined based on the identified discount and the probability that the customer will exercise the option. Amounts allocated to a material right are not recognized as revenue until, at the earliest, the option is exercised. If the options are deemed not to be a material right, they are excluded as performance obligations at the outset of the arrangement. Milestone Payments. At the inception of each arrangement that includes development milestone payments, the Company evaluates whether the milestones are considered probable of being achieved and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The Company evaluates factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to achieve the particular milestone in making this assessment. There is considerable judgment involved in determining whether it is probable that a significant revenue reversal would not occur. At the end of each subsequent reporting period, the Company reevaluates the probability of achievement of all milestones subject to constraint and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. Royalties. For arrangements that include sales-based royalties which are the result of a customer-vendor relationship and for which the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied or partially satisfied. To date, the Company has not recognized any royalty revenue resulting from any of its licensing arrangements. The Company analyzes its collaboration arrangements to assess whether such arrangements involve joint operating activities performed by parties who are both active participants in the activities and are both exposed to significant risks and rewards dependent on the commercial success of such activities. Such arrangements generally are within the scope of ASC 808, Collaborative Arrangements (ASC 808). While ASC 808 defines collaborative arrangements and provides guidance on income statement presentation, classification, and disclosures related to such arrangements, it does not address recognition and measurement matters, such as (1) determining the appropriate unit of accounting or (2) when the recognition criteria are met. Therefore, the accounting for these arrangements is either based on an analogy to other accounting literature or an accounting policy election by the Company. The Company accounts for certain components of the collaboration agreement that are reflective of a vendor-customer relationship (e.g., licensing arrangement) based on an analogy to ASC 606. The Company accounts for other components based on a reasonable, rational and consistently applied accounting policy election. Reimbursements from the counter-party that are the result of a collaborative relationship with the counter-party, instead of a customer relationship, such as co-development activities, are recorded as a reduction to research and development expense as the services are performed. For a complete discussion of accounting for revenue from collaborative and other agreements, see Note 8, Collaboration and Other Agreements.
Research and Development Costs	Research and Development Costs Research and development expenditures are expensed as incurred. Research and development costs primarily consist of employee related expenses, including salaries and benefits, expenses incurred under agreements with contract research organizations, investigative sites and consultants that conduct the Company's clinical trials, the cost of acquiring and manufacturing clinical trial materials and other allocated expenses, license fees for and milestone payments related to in-licensed products and technologies, stock-based compensation expense, and costs associated with non-clinical activities and regulatory approvals. Right-to-develop agreements may contain cost-sharing provisions whereby the Company and the collaborator share the cost of research and development activities. Reimbursement of research and development expenses received in connection with these agreements is recorded as a reduction of such expenses.
Comprehensive Loss	Comprehensive Loss Comprehensive loss represents net loss adjusted for the change during the periods attributed to unrealized gains and losses on available-for-sale securities.
Stock-based Compensation	Stock-based Compensation Stock-based payments are accounted for in accordance with the provisions of ASC 718, Compensation – Stock Compensation. The fair value of stock-based payments is estimated, on the date of grant, using the Black-Scholes model. The resulting fair value is recognized ratably over the requisite service period, which is generally the vesting period of the option. For all time-vesting awards granted, expense is amortized using the straight-line attribution method. For awards that contain a performance condition, expense is amortized using the accelerated attribution method. Recognition of stock-based compensation expense is based on the value of the portion of stock-based awards that is ultimately expected to vest during the period. The Company utilizes the Black-Scholes model for estimating fair value of its stock options granted. Option valuation models, including the Black-Scholes model, require the input of highly subjective assumptions, and changes in the assumptions used can materially affect the grant-date fair value of an award. These assumptions include the risk-free rate of interest, expected dividend yield, expected volatility and the expected life of the award.
Net Loss Per Share	Net Loss Per Share Basic loss per common share is determined by dividing loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration of common stock equivalents. Diluted loss per share is computed by dividing the loss attributable to common stockholders by the weighted-average number of common share equivalents outstanding for the period. The treasury stock method is used to determine the dilutive effect of the Company's stock option grants. 5,273,964 stock options (common stock equivalents) were excluded from the calculation of diluted net loss per share for the year ended December 31, 2018 because their inclusion would have been anti-dilutive. 4,504,642 stock options and 3,838,060 stock options were excluded from the calculation of diluted net loss per share for the years ended December 31, 2017 and 2016, respectively, because their inclusion would have been anti-dilutive.
Recently Issued Accounting Standards	Recently Issued Accounting Standards In February 2016, the FASB issued ASU No. 2016-02, Leases (ASU 2016-02) that provides principles for the recognition, measurement, presentation and disclosure of leases for both lessees and lessors. ASU 2016-02 requires a lessee to recognize assets and liabilities on the balance sheet for operating leases and changes many key definitions, including the definition of a lease. ASU 2016-02 includes a short-term lease exception for leases with an original term of 12 months or less, in which a lessee can make an accounting policy election not to recognize lease assets and lease liabilities. Lessees will continue to differentiate between finance leases (previously referred to as capital leases) and operating leases, using classification criteria that are substantially similar to the previous guidance. Originally, entities were required to adopt ASU 2016-02 using a modified retrospective transition approach for all leases existing at, or entered into after, the date of initial application. However, in July 2018, the FASB issued ASU 2018-11, Leases (Topic 842): Targeted Improvements, which now allows entities the option of recognizing the cumulative effect of applying the new standard as an adjustment to the opening balance of retained earnings in the year of adoption while continuing to present all prior periods under previous lease accounting guidance. In July 2018, the FASB also issued ASU 2018-10, Codification Improvements to Topic 842, Leases, which clarifies how to apply certain aspects of ASU 2016-02. ASU 2016-02, ASU 2018-10 and ASU 2018-11 (now commonly referred to as ASC Topic 842 (ASC 842)) is effective for the Company’s fiscal year beginning January 1, 2019. Although early adoption is permitted, the Company has not elected to do so. The Company plans to elect the transition option provided under ASU 2018-11, which will not require adjustments to comparative periods nor require modified disclosures in those comparative periods. Upon adoption, the Company expects to elect the transition package of practical expedients permitted within the new standard, which among other things, allows the carryforward of the historical lease classification. Based on its current lease portfolio, the Company estimates that the adoption ASC 842 will result in approximately $16.0 million of right of use assets and $28.0 million of lease liabilities being reflected on its consolidated balance sheet at the date of adoption. In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808)—Clarifying the interaction between Topic 808 and Topic 606 (ASU 2018-18). The amendments provide guidance on whether certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606. It also specifically (i) addresses when the participant should be considered a customer in the context of a unit of account, (ii) adds unit-of-account guidance in ASC 808 to align with guidance in ASC 606, and (iii) precludes presenting revenue from a collaborative arrangement together with revenue recognized under ASC 606 if the collaborative arrangement participant is not a customer. The guidance will be effective for fiscal years beginning after December 15, 2019. Early adoption is permitted and should be applied retrospectively. The Company does not anticipate the adoption of this standard will have a material impact on its consolidated financial statements. The Company has evaluated all other ASUs issued through the date the consolidated financials were issued and believes that the adoption of these will not have a material impact on the Company's consolidated financial statements.

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Summary of Fair Value Measurement Financial Assets

Financial assets measured at fair value on a recurring basis were as follows (in thousands):


	Fair Value Measurement at December 31, 2018
			Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds	$	46,257	$	46,257	$	—	$	—
U.S Treasury securities	12,488		—		12,488		—

Corporate debt securities	100,214		—		100,214		—
Common stock warrants	1,890		—		—		$	1,890
Total assets measured at fair value ^(a)	$	160,849	$	46,257	$	112,702	$	1,890


	Fair Value Measurement at December 31, 2017
			Quoted Prices in Active Markets for Identical Assets		Significant Other Observable Inputs		Significant Unobservable Inputs
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds	$	61,512	$	61,512	$	—	$	—
U.S Treasury securities	3,989		—		3,989		—
Government-sponsored enterprises	11,991		—		11,991		—
Corporate debt securities	78,418		—		78,418		—
Total assets measured at fair value ⁽^b)	$	155,910	$	61,512	$	94,398	$	—

(a) Total assets measured at fair value at December 31, 2018 includes approximately $146.2 million reported in cash and cash equivalents on the balance sheet.

(b) Total assets measured at fair value at December 31, 2017 includes approximately $62.5 million reported in cash and cash equivalents on the balance sheet.

Summary of Percentage of Customer Concentration

The following table includes those collaborators that represent more than 10% of total revenue earned in the periods indicated:


	Year Ended December 31,
	2018	2017		2016
Incyte Corporation (Incyte)	68%	96	%	—%
Janssen Biotech, Inc. (Janssen)	*	*		85%

Provention Bio, Inc. (Provention)	10%	—%		—%

The following table includes those counterparties that represent more than 10% of accounts receivable at the date indicated:


	December 31,
	2018	2017
Zai Lab Limited (Zai Lab)	76%	—%
Incyte	16%	—%
F. Hoffmann-La Roche Ltd and Hoffmann-La Roche Inc. (Roche)	—%	73%
Les Laboratoires Servier and Institut de Recherches Servier (Servier)	*	12%

* Balance is less than 10%

Estimated Useful Lives

Depreciation and amortization are computed using the straight-line method over the following estimated useful lives:


Computer equipment			3 years
Software			3 years
Furniture			10 years
Laboratory and office equipment			5 years
Leasehold improvements			Shorter of lease term or useful life

Schedule of New Accounting Pronouncements and Changes in Accounting Principles


	Pre-Adoption		ASC 606 Adjustment		Post-Adoption
Deferred revenue, current	$	7,202	$	540	$	7,742
Deferred revenue, net of current portion	13,637		5,939		19,576
Accumulated deficit	(312,340)		(6,478)		(318,818)

The transition adjustment resulted primarily from changes in the pattern of revenue recognition for upfront fees and license grant fees.

The following table shows the impact of adoption to the consolidated statement of income and balance sheet (in thousands):


	Year Ended December 31, 2018
	As Reported		Balances Without Adoption of ASC 606		Effect of Change Higher/(Lower)
Revenue from collaborative agreements	$	58,644	$	58,104	$	540
Net loss	(171,453)		(171,993)		(540)
Basic and diluted net loss per common share	$	(4.19)	$	(4.20)	$	0.01

	As of December 31, 2018
	As Reported		Balances Without Adoption of ASC 606		Effect of Change Higher/(Lower)
Deferred revenue, current	$	21,721	$	22,210	$	(489)
Deferred revenue, net of current portion	19,001		12,573		6,428
Accumulated deficit	(490,271)		$	(484,332)	$	(5,939)

Rollforward of Contract Liabilities

The following table presents changes in the Company’s contract liabilities during the year ended December 31, 2018 (in thousands):


	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
Deferred revenue (current and non-current)	$	27,318	$	22,992	$	(9,588)	$	40,722

- Definition

Tabular disclosure of financial instruments measured at fair value, including those classified in shareholders' equity measured on a recurring or nonrecurring basis. Disclosures include, but are not limited to, fair value measurements recorded and the reasons for the measurements, level within the fair value hierarchy in which the fair value measurements are categorized and transfers between levels 1 and 2. Nonrecurring fair value measurements are those that are required or permitted in the statement of financial position in particular circumstances.

+ References + Details

Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Stock-Based Compensation Expense

The following stock-based compensation amounts were recognized for the periods indicated (in thousands):


	Year Ended December 31,
	2018		2017		2016

Research and development	$	7,919	$	7,388	$	5,778
General and administrative	8,601		7,356		6,387
Total stock-based compensation expense	$	16,520	$	14,744	$	12,165

Schedule of Employee Stock Options Award Valuation Assumptions

The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing model using the assumptions in the following table:


	Year Ended December 31,
	2018	2017	2016
Expected dividend yield	0%	0%	0%
Expected volatility	68% - 72%	67% - 68%	64% - 69%
Risk-free interest rate	2.4% - 3.1%	1.9% - 2.3%	1.2% - 2.4%
Expected term	6.25 years	6.25 years	6.25 years

Schedule of Stock Option and Restricted Stock Unit Activity

The following table summarizes stock option activity for 2018:


	Shares	Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2017	4,504,642	$	19.79	7.0
Granted	1,269,844	27.18
Options exercised	(285,432)	4.22
Forfeited or expired	(215,090)	24.43
Outstanding, December 31, 2018	5,273,964	22.23		6.8	$	7,969

December 31, 2018:
Exercisable	3,544,139	20.60		5.9	7,969
Vested and expected to vest	5,086,009	22.10		6.7	7,969

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Components of the Company's Deferred Income Tax Assets (Liabilities)

The significant components of the Company's deferred income tax assets (liabilities) were as follows (in thousands):


	December 31,
	2018		2017
Deferred income tax assets:
Federal U.S. net operating loss carryforward	$	87,284	$	50,346
State net operating loss carryforward	22,809		7,551
Research and development credit, net	29,750		21,284
Orphan drug credit, net	22,580		21,708
Deferred rent	3,118		3,385
Deferred revenue	3,736		2,982
Depreciation	—		155
Other	6,854		5,847
Gross deferred income tax assets	176,131		113,258
Valuation allowance	(172,457)		(112,453)
Net deferred income tax assets	3,674		805

Deferred income tax liabilities:
Depreciation	(1,911)		—
Prepaid expenditures	(1,763)		(805)
Gross deferred income tax liabilities	(3,674)		(805)
Net deferred income tax asset/(liability)	$	—	$	—

Reconciliation of Reported Estimated Income Tax Benefit

The reconciliation of the reported estimated income tax benefit to the amount that would result by applying the U.S. federal statutory tax rate to the net income is as follows (in thousands):


	Year Ended December 31,
	2018		2017		2016

United States federal tax at statutory rate	$	(36,005)	$	(6,869)	$	(20,489)
State taxes (net of federal benefit)	(11,133)		(735)		(3,116)
Deferred income tax adjustments	(4,435)		607		173
Deferred state blended rate adjustments	—		(485)		(32)
Deferred federal rate change reduction in corporate rate	—		39,447		—
Research credit, net	(8,466)		(8,455)		(2,551)
Orphan drug credit, net	(872)		(1,853)		(571)
Other permanent items	148		276		145
Equity-based compensation	758		2,067		1,997
Change in valuation allowance	60,005		(24,000)		24,444
Income tax expense/(benefit)	$	—	$	—	$	—

Reconciliation of the Beginning and Ending Amount of Gross Unrecognized Tax Benefits

A reconciliation of the beginning and ending amount of gross unrecognized tax benefits is as follows (in thousands):


	Year Ended December 31,
	2018		2017		2016
Beginning balance	$	3,395	$	2,465	$	2,425
Increases for current year tax positions	642		569		308
Increases/(decreases) for prior year tax positions	281		361		(268)
Ending balance	$	4,318	$	3,395	$	2,465

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Schedule of Minimum Future Lease Payments

Future minimum lease payments under noncancelable operating leases as of December 31, 2018 are as follows (in thousands):


2019	$	6,323
2020	4,757
2021	4,724
2022	4,865
2023	4,680
Thereafter	13,786
	$	39,135

Summary of Significant Accounting Policies (Details)	12 Months Ended
Summary of Significant Accounting Policies (Details)	Dec. 31, 2018 USD ($) Segment	Dec. 31, 2017 USD ($)
Accounting Policies [Abstract]
Number of operating segments \| Segment	1
Available-for-sale securities, other than temporary impairment losses	$ 0	$ 0
Allowance recorded	0	0
Impaired assets	0	0
Assets held-for-sale		$ 0
Revenue recognized	$ (9,588,000)

Summary of Significant Accounting Policies - Summary of Fair Value Measurement Financial Asset and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Assets [Abstract]
Cash and cash equivalents	$ 146,200	$ 62,500
Securities		93,394
Common stock warrants	1,890
Total assets measured at fair value	160,849	155,910
Money market funds
Assets [Abstract]
Cash and cash equivalents	46,257	61,512
U.S Treasury securities
Assets [Abstract]
Marketable securities		3,989
Securities	12,488
Government-sponsored enterprises
Assets [Abstract]
Marketable securities		11,991
Corporate debt securities
Assets [Abstract]
Marketable securities		78,418
Securities	100,214
Quoted Prices in Active Markets for Identical Assets, Level 1
Assets [Abstract]
Common stock warrants	0
Total assets measured at fair value	46,257	61,512
Quoted Prices in Active Markets for Identical Assets, Level 1 \| Money market funds
Assets [Abstract]
Cash and cash equivalents	46,257	61,512
Quoted Prices in Active Markets for Identical Assets, Level 1 \| U.S Treasury securities
Assets [Abstract]
Marketable securities		0
Securities	0
Quoted Prices in Active Markets for Identical Assets, Level 1 \| Government-sponsored enterprises
Assets [Abstract]
Marketable securities		0
Quoted Prices in Active Markets for Identical Assets, Level 1 \| Corporate debt securities
Assets [Abstract]
Marketable securities		0
Securities	0
Significant Other Observable Inputs, Level 2
Assets [Abstract]
Common stock warrants	0
Total assets measured at fair value	112,702	94,398
Significant Other Observable Inputs, Level 2 \| Money market funds
Assets [Abstract]
Cash and cash equivalents	0	0
Significant Other Observable Inputs, Level 2 \| U.S Treasury securities
Assets [Abstract]
Marketable securities		3,989
Securities	12,488
Significant Other Observable Inputs, Level 2 \| Government-sponsored enterprises
Assets [Abstract]
Marketable securities		11,991
Significant Other Observable Inputs, Level 2 \| Corporate debt securities
Assets [Abstract]
Marketable securities		78,418
Securities	100,214
Significant Unobservable Inputs, Level 3
Assets [Abstract]
Common stock warrants	1,890
Total assets measured at fair value	1,890	0
Significant Unobservable Inputs, Level 3 \| Money market funds
Assets [Abstract]
Cash and cash equivalents	0	0
Significant Unobservable Inputs, Level 3 \| U.S Treasury securities
Assets [Abstract]
Marketable securities		0
Securities	0
Significant Unobservable Inputs, Level 3 \| Government-sponsored enterprises
Assets [Abstract]
Marketable securities		0
Significant Unobservable Inputs, Level 3 \| Corporate debt securities
Assets [Abstract]
Marketable securities		$ 0
Securities	$ 0

Summary of Significant Accounting Policies - Summary of Collaborators that Represent More Than 10% of Total Revenue Earned (Details) - Sales revenue, net - Customer Concentration Risk	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Incyte Corporation (Incyte)
Concentration Risk [Line Items]
Percentage of all significant revenue earned	68.00%	96.00%	0.00%
Janssen Biotech, Inc. (Janssen)
Concentration Risk [Line Items]
Percentage of all significant revenue earned			85.00%
Provention Bio, Inc. (Provention)
Concentration Risk [Line Items]
Percentage of all significant revenue earned	10.00%	0.00%	0.00%

Summary of Significant Accounting Policies - Summary of Collaborators that Represent More Than 10% of Accounts Receivable (Details) - Customer Concentration Risk - Accounts receivable	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Zai Lab Limited (Zai Lab)
Concentration Risk [Line Items]
Percentage of significant accounts receivable	76.00%	0.00%
Incyte Corporation (Incyte)
Concentration Risk [Line Items]
Percentage of significant accounts receivable	16.00%	0.00%
F. Hoffmann-La Roche Ltd and Hoffmann-La Roche Inc. (Roche)
Concentration Risk [Line Items]
Percentage of significant accounts receivable	0.00%	73.00%
Les Laboratoires Servier and Institut de Recherches Servier (Servier)
Concentration Risk [Line Items]
Percentage of significant accounts receivable		12.00%

Summary of Significant Accounting Policies - Estimated Useful Lives (Details)	12 Months Ended
	Dec. 31, 2018
Computer equipment
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Software
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Furniture
Property, Plant and Equipment [Line Items]
Estimated useful lives	10 years
Laboratory and office equipment
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years

Summary of Significant Accounting Policies - Adoption of 606 (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue, current	$ 21,721				$ 7,202				$ 21,721	$ 7,202		$ 7,742
Deferred revenue, net of current portion	19,001				13,637				19,001	13,637		19,576
Accumulated deficit	(490,271)				(312,340)				(490,271)	(312,340)		(318,818)
Revenues	15,794	$ 20,798	$ 18,834	$ 4,695	152,359	$ 1,663	$ 1,666	$ 2,055	60,121	157,742	$ 91,880
Net loss	(44,644)	$ (34,029)	$ (43,244)	$ (49,536)	$ 105,727	$ (47,043)	$ (40,654)	$ (37,655)	$ (171,453)	$ (19,626)	$ (58,528)
Basic and diluted net loss per common share (in usd per share)									$ (4.19)	$ (0.54)	$ (1.69)
Pre-Adoption
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue, current	22,210								$ 22,210			7,202
Deferred revenue, net of current portion	12,573								12,573			13,637
Accumulated deficit	(484,332)								(484,332)			(312,340)
Net loss									$ (171,993)
Basic and diluted net loss per common share (in usd per share)									$ (4.20)
Effect of Change Higher/(Lower)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue, current	(489)								$ (489)
Deferred revenue, net of current portion	6,428								6,428
Accumulated deficit	$ (5,939)								(5,939)
Net loss									$ (540)
Basic and diluted net loss per common share (in usd per share)									$ 0.01
Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue, current												540
Deferred revenue, net of current portion												5,939
Accumulated deficit												$ (6,478)
Revenue from collaborative agreements
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues									$ 58,644	$ 155,516	$ 86,582
Revenue from collaborative agreements \| Pre-Adoption
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues									58,104
Revenue from collaborative agreements \| Effect of Change Higher/(Lower)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues									$ 540

Summary of Signficant Accounting Policies - Contract With Customer Liability (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Accounting Policies [Abstract]
Beginning balance	$ 27,318
Additions	22,992
Deductions	(9,588)
Ending balance	$ 40,722

Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		$ 93,455
Gross Unrealized Gains		2
Gross Unrealized Losses		(63)
Fair Value		93,394
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		3,995
Gross Unrealized Gains		0
Gross Unrealized Losses		(6)
Fair Value		3,989
Government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		11,998
Gross Unrealized Gains		0
Gross Unrealized Losses		(7)
Fair Value		11,991
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 12,738	77,462
Gross Unrealized Gains	0	2
Gross Unrealized Losses	(3)	(50)
Fair Value	$ 12,735	$ 77,414

Property, Equipment and Software (Details) - USD ($)	12 Months Ended
Property, Equipment and Software (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, equipment and software	$ 94,647,000	$ 78,902,000
Construction in progress	218,000	32,800,000
Less accumulated depreciation and amortization	(37,935,000)	(28,919,000)
Property, equipment and software, net	56,712,000	49,983,000
Property and equipment purchased but not yet paid	600,000	9,600,000
Depreciation expense	9,200,000	7,000,000.0	$ 6,800,000
Computer equipment
Property, Plant and Equipment [Line Items]
Property, equipment and software	2,360,000	2,261,000
Software
Property, Plant and Equipment [Line Items]
Property, equipment and software	7,011,000	5,111,000
Furniture and office equipment
Property, Plant and Equipment [Line Items]
Property, equipment and software	668,000	656,000
Lab equipment
Property, Plant and Equipment [Line Items]
Property, equipment and software	36,062,000	20,549,000
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, equipment and software	$ 48,328,000	$ 17,525,000

Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands				12 Months Ended
	Apr. 02, 2018	May 03, 2017	Apr. 26, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Common stock, shares authorized (in shares)				125,000,000	125,000,000
Common stock, par value (in dollars per share)				$ 0.01	$ 0.01
Proceeds from issuance of common stock, net of offering costs				$ 103,259	$ 34,244	$ 0
Undesignated Preferred Stock
Class of Stock [Line Items]
Undesignated preferred stock, shares authorized (in shares)				5,000,000
Undesignated preferred stock, par value (in dollars per share)				$ 0.01
Undesignated preferred stock, shares issued (in shares)				0	0
Undesignated preferred stock, shares outstanding (in shares)				0	0
Registered Direct Offering
Class of Stock [Line Items]
Issuance of common stock, net of offering costs (in shares)			1,100,000
Number of shares issued or sold (in shares)			1,100,000
Common stock purchase price (in dollars per share)			$ 21.50
Proceeds from issuance of common stock, net of offering costs			$ 23,700
At The Market Offering
Class of Stock [Line Items]
Issuance of common stock, net of offering costs (in shares)		599,284
Number of shares issued or sold (in shares)		599,284
Common stock maximum amount available for issuance		$ 75,000
Proceeds of stock sale		$ 10,800
Firm Commitment Public Underwritten Offer
Class of Stock [Line Items]
Sale of common stock (in shares)	4,500,000
Sale of common stock (in dollars per share)	$ 21.25
Proceeds of stock sale	$ 103,000
Over-Allotment Option
Class of Stock [Line Items]
Sale of common stock (in shares)	675,000
Sale of common stock (in dollars per share)	$ 21.25

Stock-based Compensation - Employee Stock Purchase Plan (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	May 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 18, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from issuance of common stock, net of offering costs		$ 103,259	$ 34,244	$ 0
2017 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of shares authorized (in shares)					800,000
Common stock discount percent	10.00%
Percent of fair market value to purchase shares	85.00%
Common stock purchased by employees (in shares)		44,862
Proceeds from issuance of common stock, net of offering costs		$ 800

Stock-based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, options, outstanding, number (in shares)	5,273,964	4,504,642
Weighted average exercise price (in dollars per share)	$ 22.23	$ 19.79
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 16,520	$ 14,744	$ 12,165
Equity Incentive Plan 2003
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, options, outstanding, number (in shares)	746,803
Weighted average exercise price (in dollars per share)	$ 2.03
Stock Incentive Plan 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of shares authorized (in shares)				1,960,168
Increased number of shares authorized (in shares)	8,244,131
Share-based compensation arrangement by share-based payment award, options, outstanding, number (in shares)	4,527,161
Weighted average exercise price (in dollars per share)	$ 25.56
Stock reserved for future issuance (in shares)	1,960,168
Percentage of common stock share outstanding	4.00%
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 7,919	7,388	5,778
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 8,601	$ 7,356	$ 6,387

Stock-based Compensation - Option Pricing Assumptions (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%	0.00%
Expected term	6 years 3 months	6 years 3 months	6 years 3 months
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	68.00%	67.00%	64.00%
Risk-free interest rate	2.40%	1.90%	1.20%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	72.00%	68.00%	69.00%
Risk-free interest rate	3.10%	2.30%	2.40%
Options granted, maximum term	10 years

Stock-based Compensation - Stock Option and Restricted Stock Unit Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares
December 31, 2016	4,504,642
Granted	1,269,844
Options exercised or RSUs vested	(285,432)
Forfeited or expired	(215,090)
December 31, 2017	5,273,964	4,504,642
Exercisable	3,544,139
Vested and expected to vest	5,086,009
Weighted-Average Exercise Price
December 31, 2016	$ 19.79
Granted	27.18
Options exercised or RSUs vested	4.22
Forfeited or expired	24.43
December 31, 2017	22.23	$ 19.79
Exercisable	20.60
Vested and expected to vest	$ 22.10
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-average remaining contractual term, Outstanding	6 years 9 months 18 days	7 years
Weighted-average remaining contractual term, Exercisable	5 years 10 months 24 days
Weighted-average remaining contractual term, Vested and expected to vest	6 years 8 months 12 days
Aggregate intrinsic value, Outstanding	$ 7,969
Aggregate intrinsic value, Exercisable	7,969
Aggregate intrinsic value, Vested and expected to vest	$ 7,969
Common stock, shares issued (in shares)	274,362	253,036	526,715
Cash proceeds from exercise of stock options	$ 900	$ 500	$ 1,900
Weighted-average grant-date fair value of options granted (in dollars per share)	$ 17.90	$ 12.53	$ 15.17
Share-based compensation arrangement by share-based payment award, options, exercises in period, intrinsic value	$ 5,200	$ 4,200	$ 10,800
Fair value of shares vested	16,400	$ 14,600	$ 11,600
Unrecognized compensation cost related to non-vested stock-based compensation arrangements	$ 24,200
Unrecognized compensation expense recognition period	2 years 7 months 6 days

Income Taxes - Components of the Company's Deferred Tax Assets (Liabilities) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Provision for federal or state income taxes	$ 0	$ 0	$ 0
Deferred income tax assets:
Federal U.S. net operating loss carryforward	87,284,000	50,346,000
State net operating loss carryforward	22,809,000	7,551,000
Research and development credit, net	29,750,000	21,284,000
Orphan drug credit, net	22,580,000	21,708,000
Deferred rent	3,118,000	3,385,000
Deferred revenue	3,736,000	2,982,000
Depreciation	0	155,000
Other	6,854,000	5,847,000
Gross deferred income tax assets	176,131,000	113,258,000
Valuation allowance	(172,457,000)	(112,453,000)
Net deferred income tax assets	3,674,000	805,000
Deferred income tax liabilities:
Depreciation	(1,911,000)	0
Prepaid expenditures	(1,763,000)	(805,000)
Gross deferred income tax liabilities	(3,674,000)	(805,000)
Net deferred income tax asset/(liability)	0	$ 0
Operating Loss Carryforwards [Line Items]
Remaining portion of net operating losses	402,100,000
Previously unrecognized excess tax benefits	18,600,000
Previously unrecognized excess tax benefits, tax effected portion	6,500,000
U.S. Federal and State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	415,600,000
U.S. Federal Government
Operating Loss Carryforwards [Line Items]
US Federal tax credits carry forward	52,300,000
Net operating loss for limited use	13,500,000
U.S. Federal Government \| Minimum
Operating Loss Carryforwards [Line Items]
Net operating losses limited for use utilized on an annual basis	200,000
U.S. Federal Government \| Maximum
Operating Loss Carryforwards [Line Items]
Net operating losses limited for use utilized on an annual basis	1,400,000
Tax Year 2025 To 2037 \| U.S. Federal and State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	237,800,000
Indefinite \| U.S. Federal and State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 177,800,000

Income Taxes - Reconciliation of Reported Estimated Income Tax Benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
United States federal tax at statutory rate	$ (36,005)	$ (6,869)	$ (20,489)
State taxes (net of federal benefit)	(11,133)	(735)	(3,116)
Deferred income tax adjustments	(4,435)	607	173
Deferred state blended rate adjustments	0	(485)	(32)
Deferred federal rate change reduction in corporate rate	0	39,447	0
Research credit, net	(8,466)	(8,455)	(2,551)
Orphan drug credit, net	(872)	(1,853)	(571)
Other permanent items	148	276	145
Equity-based compensation	758	2,067	1,997
Change in valuation allowance	60,005	(24,000)	24,444
Income tax expense/(benefit)	$ 0	$ 0	$ 0

Income Taxes - Reconciliation of the Beginning and Ending Amount of Gross Unrecognized Tax Benefits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 3,395,000	$ 2,465,000	$ 2,425,000
Increases for current year tax positions	642,000	569,000	308,000
Increases for prior year tax positions	281,000	361,000
Decreases for prior year tax positions			(268,000)
Ending balance	4,318,000	3,395,000	2,465,000
Gross unrecognized tax benefits	$ 4,500,000	3,400,000
Unrecognized interest or penalties		$ 0	$ 0

Collaboration and Other Agreements, Incyte Corporation (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Oct. 31, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Collaboration and Other Agreements [Line Items]
Revenues		$ 15,794	$ 20,798	$ 18,834	$ 4,695	$ 152,359	$ 1,663	$ 1,666	$ 2,055	$ 60,121	$ 157,742	$ 91,880
Incyte MGA012 Agreement \| Incyte Corporation (Incyte)
Collaboration and Other Agreements [Line Items]
Non-refundable upfront payment						$ 150,000
Amounts recognized										15,000
Transaction price	$ 154,000
Clinical trial activities selling price amount	4,000
Maximum \| Incyte MGA012 Agreement \| Incyte Corporation (Incyte)
Collaboration and Other Agreements [Line Items]
Potential development and regulatory milestone payments	420,000
Potential commercial milestone payments	$ 330,000
Potential proceeds from royalties percent	24.00%
Minimum \| Incyte MGA012 Agreement \| Incyte Corporation (Incyte)
Collaboration and Other Agreements [Line Items]
Potential proceeds from royalties percent	15.00%
Revenues From License Agreements \| Incyte MGA012 Agreement \| Incyte Corporation (Incyte)
Collaboration and Other Agreements [Line Items]
Revenues										18,800	$ 151,100
Revenues From License Agreements \| Incyte MGA012 Clinical Services \| Incyte Corporation (Incyte)
Collaboration and Other Agreements [Line Items]
Revenues										$ 22,200

Collaboration and Other Agreements, Zai Lab (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Nov. 30, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Collaboration and Other Agreements [Line Items]
Revenues		$ 15,794	$ 20,798	$ 18,834	$ 4,695	$ 152,359	$ 1,663	$ 1,666	$ 2,055	$ 60,121	$ 157,742	$ 91,880
Deferred revenue		40,722				$ 27,318				40,722	$ 27,318
Zai Lab Agreement \| Zai Lab
Collaboration and Other Agreements [Line Items]
Non-refundable upfront payment	$ 25,000
Tax withholding	$ 2,500
Potential development and regulatory milestone payments		140,000								140,000
Revenues										1,300
Deferred revenue		21,100								21,100
Deferred revenue, current		$ 16,100								$ 16,100

Collaboration and Other Agreements, Servier (Details) - USD ($)	1 Months Ended	3 Months Ended								12 Months Ended
	Sep. 30, 2012	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018	Dec. 31, 2015
Collaboration and Other Agreements [Line Items]
Revenues		$ 15,794,000	$ 20,798,000	$ 18,834,000	$ 4,695,000	$ 152,359,000	$ 1,663,000	$ 1,666,000	$ 2,055,000	$ 60,121,000	$ 157,742,000	$ 91,880,000
Deferred revenue included in current liabilities		21,721,000				7,202,000				21,721,000	7,202,000		$ 7,742,000
Deferred revenue		40,722,000				27,318,000				40,722,000	27,318,000
Increase in revenue recognized from ASC 606 adoption										9,588,000
Servier \| Servier DART
Collaboration and Other Agreements [Line Items]
Non-refundable upfront payment	$ 20,000,000.0
Milestone payment removed	5,000,000.0
Option exercise fee														$ 15,000,000.0
Offset to research and development costs under collaboration arrangement										6,000,000.0	3,200,000	2,600,000
Deferred revenue		12,600,000								12,600,000
Deferred revenue, current		900,000								900,000
Deferred revenue, noncurrent		11,700,000								11,700,000
Deferred revenue						7,400,000					7,400,000
Increase in balance related to adoption of ASC 606										6,400,000
Increase in revenue recognized from ASC 606 adoption										100,000
Servier \| Maximum \| Servier DART
Collaboration and Other Agreements [Line Items]
Potential clinical milestone payments under agreement	22,500,000
Potential regulatory milestone payments under agreement	76,000,000.0
Potential sales milestone payments under agreement	$ 210,000,000.0
Revenues From License Agreements \| Servier \| Servier DART
Collaboration and Other Agreements [Line Items]
Revenues										1,200,000	1,400,000	2,200,000
Revenues From License Agreements \| Servier \| Servier Agreement - MGD007 Option
Collaboration and Other Agreements [Line Items]
Revenues										1,900,000	1,100,000	$ 1,100,000
Deferred revenue included in current liabilities						$ 1,100,000					$ 1,100,000
Deferred revenue		$ 0								$ 0

Collaboration and Other Agreements, Roche (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended								12 Months Ended
	Jan. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Collaboration and Other Agreements [Line Items]
Revenues			$ 15,794	$ 20,798	$ 18,834	$ 4,695	$ 152,359	$ 1,663	$ 1,666	$ 2,055	$ 60,121	$ 157,742	$ 91,880
Deferred revenue		$ 27,318	40,722				27,318				40,722	27,318
Deferred revenue included in current liabilities		7,202	21,721				7,202				21,721	7,202		$ 7,742
Deferred revenue included in long-term liabilities		$ 13,637	19,001				13,637				19,001	13,637		$ 19,576
Roche
Collaboration and Other Agreements [Line Items]
Non-refundable upfront payment	$ 10,000
Potential milestone payments and royalties on future sales			370,000								370,000
Expected period of development		30 months
Revenues											4,000
Deferred revenue			6,000								6,000
Deferred revenue, current			4,000								4,000
Deferred revenue, noncurrent			$ 2,000								$ 2,000
Deferred revenue		$ 10,000					10,000					10,000
Deferred revenue included in current liabilities		4,000					4,000					4,000
Deferred revenue included in long-term liabilities		$ 6,000					$ 6,000					$ 6,000

Collaboration and Other Agreements, Provention (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	May 31, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Collaboration and Other Agreements [Line Items]
Revenues		$ 15,794	$ 20,798	$ 18,834	$ 4,695	$ 152,359	$ 1,663	$ 1,666	$ 2,055	$ 60,121	$ 157,742	$ 91,880
Provention Bio, Inc. (Provention)
Collaboration and Other Agreements [Line Items]
Transaction price	$ 6,100
Stock warrants (in shares)	2,432,688
Fair Value Adjustment of Warrants										$ 4,200
Provention License Agreement \| Provention PRV3279 \| Provention Bio, Inc. (Provention)
Collaboration and Other Agreements [Line Items]
Consideration received common stock warrant exercise price (in usd per share)	$ 2.50
Potential development and regulatory milestone payments	$ 65,000
Potential commercial milestone payments	$ 225,000
Asset Purchase Agreement \| Provention PRV031 \| Provention Bio, Inc. (Provention)
Collaboration and Other Agreements [Line Items]
Consideration received common stock warrant exercise price (in usd per share)	$ 2.50
Potential development and regulatory milestone payments	$ 170,000
Potential commercial milestone payments	225,000
Potential milestone payment to third parties for intellectual property under agreement	1,300
Revenues From License Agreements \| Provention Bio, Inc. (Provention)
Collaboration and Other Agreements [Line Items]
Revenues	$ 6,100

Collaboration and Other Agreements, Janssen Biotech, Inc. (Details) - USD ($) $ in Thousands	1 Months Ended			3 Months Ended								12 Months Ended
	Jul. 31, 2016	Jan. 31, 2015	Dec. 31, 2014	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Collaboration and Other Agreements [Line Items]
Revenues				$ 15,794	$ 20,798	$ 18,834	$ 4,695	$ 152,359	$ 1,663	$ 1,666	$ 2,055	$ 60,121	$ 157,742	$ 91,880
Janssen MGD011 Agreement \| Janssen Biotech Inc.
Collaboration and Other Agreements [Line Items]
Sale of common stock (in shares)			1,923,077
Proceeds of stock sale		$ 75,000	$ 75,000
Non-refundable upfront payment														50,000
Janssen MGD015 Agreement \| Janssen Biotech Inc.
Collaboration and Other Agreements [Line Items]
Non-refundable upfront payment	$ 75,000
Revenues From License Agreements \| Janssen MGD011 Agreement \| Janssen Biotech Inc.
Collaboration and Other Agreements [Line Items]
Revenues												0		2,000
Revenues From License Agreements \| Janssen MGD015 Agreement \| Janssen Biotech Inc.
Collaboration and Other Agreements [Line Items]
Revenues												$ 0	$ 600	$ 75,800

Collaboration and Other Agreements, NIAID Contract (Details)		3 Months Ended								12 Months Ended
	Sep. 15, 2015 USD ($) Molecule	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Collaboration and Other Agreements [Line Items]
Revenues		$ 15,794,000	$ 20,798,000	$ 18,834,000	$ 4,695,000	$ 152,359,000	$ 1,663,000	$ 1,666,000	$ 2,055,000	$ 60,121,000	$ 157,742,000	$ 91,880,000
NIAID
Collaboration and Other Agreements [Line Items]
Commercialization of molecules \| Molecule	2
Base period value	$ 7,500,000
Proceeds from additional development funding options under agreement										10,800,000
NIAID \| Maximum
Collaboration and Other Agreements [Line Items]
Additional development funding options	17,000,000.0
Total potential value	$ 24,500,000
Revenues From License Agreements \| NIAID
Collaboration and Other Agreements [Line Items]
Revenues										$ 1,300,000	$ 1,700,000	$ 5,100,000

Commitments and Contingencies (Details) $ in Thousands		1 Months Ended	12 Months Ended
Commitments and Contingencies (Details) $ in Thousands	Jul. 21, 2017 USD ($)	Jul. 31, 2015 USD ($)	Dec. 31, 2018 USD ($) Lease	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Number of leases \| Lease			5
Future sublease payments to be received			$ 1,100
Lease incentives	$ (7,500)	$ (5,100)
Deferred rent liability			11,300	$ 12,300
Rent expense			4,400	$ 3,100	$ 3,000
Future minimum rental payments required under all non-cancelable operating leases [Abstract]
2019			6,323
2020			4,757
2021			4,724
2022			4,865
2023			4,680
Thereafter			13,786
Total			$ 39,135

Employee Benefit Plan (Details) - USD ($) $ in Millions	12 Months Ended
Employee Benefit Plan (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2012
Retirement Benefits [Abstract]
Eligible age to participate in plan				21 years
Percentage of employee contribution to salary				100.00%
Percentage of employee vested contribution	100.00%
Defined contribution plan, employer discretionary contribution amount	$ 1.3	$ 1.1	$ 1.0

Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 15,794	$ 20,798	$ 18,834	$ 4,695	$ 152,359	$ 1,663	$ 1,666	$ 2,055	$ 60,121	$ 157,742	$ 91,880
Net loss	$ (44,644)	$ (34,029)	$ (43,244)	$ (49,536)	$ 105,727	$ (47,043)	$ (40,654)	$ (37,655)	$ (171,453)	$ (19,626)	$ (58,528)
Net loss per share, basic and diluted (in usd per share)	$ (1.06)	$ (0.81)	$ (1.03)	$ (1.34)
Net income (loss) per share, basic (in dollars per share)					$ 2.87	$ (1.28)	$ (1.14)	$ (1.08)
Net income (loss) per share, diluted (in dollars per share)					$ 2.80	$ (1.28)	$ (1.14)	$ (1.08)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	12 Months Ended
	Apr. 02, 2018	Feb. 28, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Subsequent Event [Line Items]
Proceeds from issuance of common stock, net of offering costs			$ 103,259	$ 34,244	$ 0
Follow Up Offering \| Subsequent Event
Subsequent Event [Line Items]
Sale of common stock (in shares)		5,500,000
Proceeds from issuance of common stock, net of offering costs		$ 118,500
Sale of common stock (in dollars per share)		$ 20.00
Over-Allotment Option
Subsequent Event [Line Items]
Sale of common stock (in shares)	675,000
Sale of common stock (in dollars per share)	$ 21.25
Over-Allotment Option \| Subsequent Event
Subsequent Event [Line Items]
Sale of common stock (in shares)		825,000
Sale of common stock (in dollars per share)		$ 20.00

Organization and Nature of Operations	12 Months Ended
Organization and Nature of Operations	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Nature of Operations	Organization and Nature of OperationsMacroGenics, Inc. (the Company) is incorporated in the state of Delaware. The Company is a biopharmaceutical company focused on discovering and developing innovative antibody-based therapeutics designed to modulate the human immune response for the treatment of cancer. The Company currently has a pipeline of product candidates in human clinical testing that have been created primarily using its proprietary technology platforms. The Company believes its programs have the potential to have a meaningful effect on treating patients' unmet medical needs as monotherapy or, in some cases, in combination with other therapeutic agents.

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Event	Subsequent EventIn February 2019, the Company completed a follow-on equity offering, in which the Company sold 5,500,000 shares of its common stock at a price of $20.00 per share. Additionally, the underwriters of the offering exercised the full amount of their over-allotment option resulting in the sale of an additional 825,000 shares of the Company’s common stock at a price of $20.00 per share. The Company received net proceeds of $118.5 million from this offering, net of underwriting discounts and commissions and other estimated offering expenses.

Employee Benefit Plan	12 Months Ended
Employee Benefit Plan	Dec. 31, 2018
Retirement Benefits [Abstract]
Employee Benefit Plan	Employee Benefit PlanIn 2002, the Company established the MacroGenics 401(k) Plan (the Plan) for its employees under Section 401(k) of the IRC. Under this Plan, all employees at least 21 years of age are eligible to participate in the Plan, starting on the first day of each month. Employees may contribute up to 100% of their salary, subject to government maximums.Employees are 100% vested in their contributions to the Plan. The Company's contribution to the Plan, as determined by the Board of Directors, is discretionary. The Company's contributions to the Plan totaled $1.3 million, $1.1 million and $1.0 million for the years ended December 31, 2018, 2017 and 2016, respectively.