MacroGenics (MGNX) 10-Q 31 Jul 19 2019 Q2 Quarterly report Financial data

Cover Page

Cover Page - shares	6 Months Ended
	Jun. 30, 2019	Jul. 26, 2019
Cover page.
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Jun. 30, 2019
Entity File Number	001-36112
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Entity Registrant Name	MACROGENICS, INC.
Entity Central Index Key	0001125345
Current Fiscal Year End Date	--12-31
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Title of 12(b) Security	Common Stock, par value $0.01 per share
Entity Small Business	false
Local Phone Number	251-5172
City Area Code	301
Trading Symbol	MGNX
Security Exchange Name	NASDAQ
Entity Address, Postal Zip Code	20850
Entity Tax Identification Number	06-1591613
Entity Incorporation, State or Country Code	DE
Entity Common Stock, Shares Outstanding		48,893,451
Entity Address, Address Line One	9704 Medical Center Drive
Entity Address, City or Town	Rockville
Entity Address, State or Province	MD
Amendment Flag	false
Entity Shell Company	false

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 180,316	$ 220,128
Marketable securities	91,820	12,735
Accounts receivable	5,613	29,583
Prepaid expenses	9,616	6,406
Other current assets	232	272
Total current assets	287,597	269,124
Property, equipment and software, net	52,295	56,712
Other assets	43,785	6,294
Total assets	383,677	332,130
Current liabilities:
Accounts payable	857	4,005
Accrued expenses	30,410	33,021
Deferred revenue	14,449	21,721
Deferred rent	0	1,018
Lease liabilities	3,644	0
Other current liabilities	175	175
Total current liabilities	49,535	59,940
Deferred revenue, net of current portion	15,413	19,001
Lease liabilities, net of current portion	24,278	0
Deferred rent, net of current portion	0	10,312
Total liabilities	89,226	89,253
Stockholders' equity:
Common stock, $0.01 par value -- 125,000,000 shares authorized, 48,893,451 and 42,353,301 shares outstanding at June 30, 2019 and December 31, 2018, respectively	489	424
Additional paid-in capital	860,983	732,727
Accumulated other comprehensive income (loss)	34	(3)
Accumulated deficit	(567,055)	(490,271)
Total stockholders' equity	294,451	242,877
Total liabilities and stockholders' equity	$ 383,677	$ 332,130

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Stockholders' equity:
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)	48,893,451	42,353,301

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues:
Revenues	$ 10,593	$ 18,834	$ 20,255	$ 23,529
Costs and expenses:
Research and development	51,440	52,014	98,500	97,684
General and administrative	12,122	11,134	22,341	20,369
Total costs and expenses	63,562	63,148	120,841	118,053
Loss from operations	(52,969)	(44,314)	(100,586)	(94,524)
Other income	21,202	1,070	23,802	1,744
Net loss	(31,767)	(43,244)	(76,784)	(92,780)
Other comprehensive income:
Unrealized gain on investments	34	40	37	79
Comprehensive loss	$ (31,733)	$ (43,204)	$ (76,747)	$ (92,701)
Basic and diluted net loss per common share (in usd per share)	$ (0.65)	$ (1.03)	$ (1.63)	$ (2.35)
Basic and diluted weighted average common shares outstanding (in shares)	48,845,234	42,153,813	47,234,889	39,559,599
Revenue From Collaborative Agreements
Revenues:
Revenues	$ 9,987	$ 18,552	$ 19,484	$ 23,053
Revenue From Government Agreements
Revenues:
Revenues	$ 606	$ 282	$ 771	$ 476

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2017		36,859,077
Beginning balance at Dec. 31, 2017	$ 299,238	$ 369	$ 611,270	$ (312,340)	$ (61)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	3,386		3,386
Stock plan related activity	629	$ 1	628
Stock plan related activity (in shares)		165,546
Unrealized gain on investments	38				38
Net loss	(49,536)			(49,536)
Ending balance (in shares) at Mar. 31, 2018		37,024,623
Ending balance at Mar. 31, 2018	247,276	$ 370	615,284	(368,355)	(23)
Beginning balance (in shares) at Dec. 31, 2017		36,859,077
Beginning balance at Dec. 31, 2017	299,238	$ 369	611,270	(312,340)	(61)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(92,780)
Ending balance (in shares) at Jun. 30, 2018		42,229,011
Ending balance at Jun. 30, 2018	312,036	$ 422	723,196	(411,599)	17
Beginning balance (in shares) at Mar. 31, 2018		37,024,623
Beginning balance at Mar. 31, 2018	247,276	$ 370	615,284	(368,355)	(23)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	4,209		4,209
Issuance of common stock, net of offering costs (in shares)		5,175,000
Issuance of common stock, net of offering costs	103,259	$ 52	103,207
Stock plan related activity	496		496
Stock plan related activity (in shares)		29,388
Unrealized gain on investments	40				40
Net loss	(43,244)			(43,244)
Ending balance (in shares) at Jun. 30, 2018		42,229,011
Ending balance at Jun. 30, 2018	312,036	$ 422	723,196	(411,599)	17
Beginning balance (in shares) at Dec. 31, 2018		42,353,301
Beginning balance at Dec. 31, 2018	242,877	$ 424	732,727	(490,271)	(3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	3,750		3,750
Issuance of common stock, net of offering costs (in shares)		6,325,000
Issuance of common stock, net of offering costs	118,657	$ 63	118,594
Stock plan related activity	347	$ 1	346
Stock plan related activity (in shares)		126,707
Unrealized gain on investments	3				3
Net loss	(45,017)			(45,017)
Ending balance (in shares) at Mar. 31, 2019		48,805,008
Ending balance at Mar. 31, 2019	320,617	$ 488	855,417	(535,288)	0
Beginning balance (in shares) at Dec. 31, 2018		42,353,301
Beginning balance at Dec. 31, 2018	$ 242,877	$ 424	732,727	(490,271)	(3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock plan related activity (in shares)	1,796,645
Net loss	$ (76,784)
Ending balance (in shares) at Jun. 30, 2019		48,893,451
Ending balance at Jun. 30, 2019	294,451	$ 489	860,983	(567,055)	34
Beginning balance (in shares) at Mar. 31, 2019		48,805,008
Beginning balance at Mar. 31, 2019	320,617	$ 488	855,417	(535,288)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	4,933		4,933
Stock plan related activity	634	$ 1	633
Stock plan related activity (in shares)		88,443
Unrealized gain on investments	34				34
Net loss	(31,767)			(31,767)
Ending balance (in shares) at Jun. 30, 2019		48,893,451
Ending balance at Jun. 30, 2019	$ 294,451	$ 489	$ 860,983	$ (567,055)	$ 34

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities
Net loss	$ (76,784)	$ (92,780)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	5,483	2,540
Stock-based compensation	8,683	7,595
Changes in operating assets and liabilities:
Accounts receivable	23,971	(4,194)
Prepaid expenses	(3,209)	(22)
Other assets	(21,091)	(5,511)
Accounts payable	(2,598)	(684)
Accrued expenses	(2,663)	8,215
Lease exit liability	0	(298)
Deferred revenue	(10,861)	(3,371)
Lease liabilities	231	0
Deferred rent	0	(516)
Net cash used in operating activities	(78,838)	(89,026)
Cash flows from investing activities
Purchases of marketable securities	(142,305)	(86,491)
Proceeds from sale and maturities of marketable securities	63,955	118,090
Purchases of property and equipment	(2,262)	(20,023)
Net cash provided by (used in) investing activities	(80,612)	11,576
Cash flows from financing activities
Proceeds from issuance of common stock, net of offering costs	118,657	103,259
Proceeds from stock option exercises and ESPP purchases	981	1,125
Net cash provided by financing activities	119,638	104,384
Net change in cash and cash equivalents	(39,812)	26,934
Cash and cash equivalents at beginning of period	220,128	211,727
Cash and cash equivalents at end of period	180,316	238,661
Supplemental Cash Flow Information [Abstract]
Right-of-use assets modified in exchange for operating lease obligations	$ 1,988	$ 0

Details

Details - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Statement of Cash Flows [Abstract]
Fair value of warrants received, including change in value	$ 0	$ 6,130

Basis of Presentation and Signi

Basis of Presentation and Significant Accounting Policies	6 Months Ended
	Jun. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Significant Accounting Policies	Basis of Presentation and Significant Accounting Policies Basis of Presentation The accompanying unaudited interim consolidated financial statements of MacroGenics, Inc. (the Company) have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information. The financial statements include all adjustments (consisting only of normal recurring adjustments) that the management of the Company believes are necessary for a fair presentation of the periods presented. These interim financial results are not necessarily indicative of results expected for the full fiscal year or for any subsequent interim period. The accompanying unaudited interim 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. These consolidated financial statements and related notes should be read in conjunction with the financial statements and notes thereto included in the Company's 2018 Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) on February 26, 2019. Summary of Significant Accounting Policies With the exception of the adoption of Accounting Standards Update (ASU) No. 2016-02, Leases (ASU 2016-02) during the six months ended June 30, 2019, discussed below, there have been no material changes to the significant accounting policies previously disclosed in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018. Recent Accounting Pronouncements Recently Adopted Accounting Standards In February 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-02, which requires lessees to recognize a right-of-use (ROU) asset and a lease liability for all leases with terms greater than 12 months and also requires disclosures by lessees and lessors about the amount, timing and uncertainty of cash flows arising from leases. Subsequent to the issuance of ASU 2016-02, the FASB clarified the guidance through several ASUs, with the resulting guidance collectively referred to as ASC 842. The Company adopted ASC 842 effective January 1, 2019, using the optional transition method provided under ASU 2018-11, which did not require adjustments to comparative periods nor require modified disclosures in those comparative periods. The Company has elected not to recognize leases with terms of one year or less on the balance sheet. At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances. For leases where the Company is the lessee, ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent an obligation to make lease payments arising from the lease. ROU assets and lease liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. The interest rate implicit in lease contracts is typically not readily determinable. As such, the Company utilizes the appropriate incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term of the lease for which the rate is estimated. Certain adjustments to the ROU asset may be required for items such as initial direct costs paid or incentives received. The lease terms used to calculate the ROU asset and related lease liabilities include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense for operating leases is recognized on a straight-line basis over the lease term as an operating expense while the expense for finance leases is recognized as depreciation expense and interest expense using the accelerated interest method of recognition. The Company has lease agreements which require payments for lease and non-lease components and has elected the practical expedient not to separate non-lease components from lease components for all classes of underlying assets. As a result of the cumulative impact of adopting ASC 842, the Company recorded operating lease ROU assets of $16.4 million and operating lease liabilities of $27.7 million as of January 1, 2019, primarily related to real estate leases, based on the present value of the future lease payments on the date of adoption. The ROU asset is included in Other assets on the consolidated balance sheets. Refer to Note 4, Leases, for additional disclosures required by ASC 842. Recently Issued Accounting Standards 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.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
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, accrued expenses and common stock warrants. 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 Financial Accounting Standards Board 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 Measurements at June 30, 2019 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 $ 55,663 $ 55,663 $ — $ — Government-sponsored enterprises 20,927 — 20,927 — Corporate debt securities 84,356 — 84,356 — Common stock warrants 22,356 — — 22,356 Total assets measured at fair value (a) $ 183,302 $ 55,663 $ 105,283 $ 22,356 Fair Value Measurements 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 (b) $ 160,849 $ 46,257 $ 112,702 $ 1,890 (a) Total assets measured at fair value at June 30, 2019 includes approximately $69.1 million reported in cash and cash equivalents and $22.4 million reported in other assets on the balance sheet. (b) 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 and $1.9 million reported in other assets 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.

Marketable Securities

Marketable Securities	6 Months Ended
	Jun. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	Marketable Securities Available-for-sale marketable securities as of June 30, 2019 and December 31, 2018 were as follows (in thousands): June 30, 2019 Amortized Gross Gross Fair Government-sponsored enterprises $ 20,919 $ 8 $ — $ 20,927 Corporate debt securities 70,867 26 — 70,893 Total $ 91,786 $ 34 $ — $ 91,820 December 31, 2018 Amortized Gross Gross Fair Corporate debt securities $ 12,738 $ — $ (3) $ 12,735 All available-for-sale marketable securities held as of June 30, 2019 and December 31, 2018 had contractual maturities of less than one year. All of the Company's available-for-sale marketable securities in an unrealized loss position as of June 30, 2019 and December 31, 2018 were in a loss position for less than 12 months. There were no unrealized losses at June 30, 2019 or December 31, 2018 that the Company determined to be other-than-temporary.

Leases

Leases	6 Months Ended
	Jun. 30, 2019
Leases [Abstract]
Leases	Leases The Company has non-cancelable operating leases for manufacturing, laboratory and office space in Rockville, Maryland and a non-cancelable operating lease for laboratory and office space in Brisbane, California. A portion of the space under one of these leases is subleased to a third party. All of these leases include one or more options to renew, with those renewal periods ranging from five Upon adoption of ASC 842 on January 1, 2019, it was not reasonably certain that the Company would extend any of its operating leases, therefore the options to extend the lease terms were not recognized as part of the ROU assets or lease liabilities. During the three months ended March 31, 2019, the Company determined that it would exercise the option to extend one lease for an additional five six months ended June 30, 2019. As of June 30, 2019, the Company’s ROU assets were valued at $17.1 million and are included in Other assets on the consolidated balance sheet. The components of lease cost for the six months ended June 30, 2019 were as follows (in thousands): Operating lease cost $ 2,701 Variable lease cost 618 Sublease income (471) Net lease cost $ 2,848 As of June 30, 2019, the maturities of our operating lease liabilities were as follows (in thousands): Remainder of 2019 $ 3,201 2020 5,603 2021 5,291 2022 5,450 2023 5,279 2024 4,293 Thereafter 10,081 Total lease payments 39,198 Present value adjustment (11,276) Lease liabilities $ 27,922

Stockholders' Equity

Stockholders' Equity	6 Months Ended
	Jun. 30, 2019
Equity [Abstract]
Stockholders' Equity	Stockholders' Equity In April 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. In February 2019, the Company completed a firm-commitment underwritten public 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 approximately $118.7 million from this offering, net of underwriting discounts and commissions and other offering expenses.

Collaboration and Other Agreeme

Collaboration and Other Agreements	6 Months Ended
	Jun. 30, 2019
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 Corporation (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 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. Through December 31, 2018, the Company had recognized $15.0 million in development milestones under this agreement. If MGA012 is 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. The Company evaluated the Incyte Agreement under the provisions of ASU No. 2014-09, Revenue from Contracts with Customer s and all related amendments (collectively, 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 is performing 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 the 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 deve lopment 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. During the three and six months ended June 30, 2019 and 2018, there were no adjustments to the transaction price of the Incyte Agreemen t. The Company recognized the $150.0 million allocated to the license when it satisfied its performance obligation and transferred the license to Incyte in 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. During the three months ended June 30, 2019 and 2018, the Company recognized no revenue and revenue of $0.6 million, respectively, under the Incyte Agreement. The Company recognized revenue of $0.1 million and $3.1 million under the Incyte Agreement during the six months ended June 30, 2019 and 2018, respectively. The Company also has an agreement with Incyte, which was entered into in 2018, under which the Company is to perform development and manufacturing services for Incyte’s clinical needs of MGA012. The Company evaluated the 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 three months ended June 30, 2019 and 2018, the Company recognized revenue of $4.2 million and $9.9 million, respectively, for services performed under this agreement. The Company recognized revenue of $8.2 million and $9.9 million for services performed under this agreement during the six months ended June 30, 2019 and 2018, respectively. Les Laboratoires Servier In September 2012, the Company entered into a collaboration agreement with Les Laboratoires Servier and Institut de Recherches Servier (collectively, 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). In 2014, Servier exercised its exclusive option to develop and commercialize flotetuzumab. In 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. In July 2019, Servier informed the Company of its intention to terminate the Servier Agreement effective January 15, 2020, unless sooner agreed to by the parties. Upon execution of the agreement, Servier made a nonrefundable payment of $20.0 million to the Company. 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 Investigational New Drug (IND) applications for flotetuzumab and MGD007 were cleared by the Food and Drug Administration (FDA). Upon achievement of each milestone in 2014, 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 was recognized as the research and development services were provided using a cost-based input method according to research and development costs incurred to date compared to estimated total research and development costs. The transfer of control occurred over this time period and, in management’s judgment, was the best measure of progress towards satisfying the performance obligation. All revenue related to the upfront payment was recognized by December 31, 2018. The Company recognized no revenue during the three and six months ended June 30, 2019 related to the upfront payment, and recognized $0.4 million and $0.9 million in revenue during the three and six months ended June 30, 2018, respectively, related to the transaction price allocated to the MGD007 option. No revenue was deferred at December 31, 2018 or June 30, 2019. 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 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, Collaborative Arrangements (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 is recognizing 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. During each of the three month periods ended June 30, 2019 and 2018, the Company recognized revenue of $0.3 million related to the flotetuzumab license grant fee. The Company recognized revenue related to the flotetuzumab license grant fee of $0.5 million and $0.6 million during the six months ended June 30, 2019 and 2018, respectively. At June 30, 2019, $12.1 million of revenue related to the flotetuzumab license grant fee was deferred, $1.7 million of which was current and $10.4 million of which was non-current. 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 follows its policy to record expense incurred as research and development expense and reimbursements received from Servier are 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 months ended June 30, 2019 and 2018, the Company recorded approximately $1.2 million and $1.6 million, respectively, as an offset to research and development expense under this collaborative arrangement. During the six months ended June 30, 2019 and 2018, the Company recorded approximately $2.0 million and $2.8 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-enhancing 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 $2.5 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 each performance obligation 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 three and six months ended June 30, 2019, the Company recognized revenue of $4.0 million and $8.0 million, respectively, related to the Zai Lab Agreement. At June 30, 2019, $13.1 million of revenue was deferred under this agreement, $8.1 million of which was current and $5.0 million of which was non-current. At December 31, 2018, $21.1 million of revenue was deferred under this agreement, $16.1 million of which was current and $5.0 million of which was non-current. Roche In December 2017, the Company entered into a research collaboration and license agreement with F. Hoffmann-La Roche Ltd and Hoffmann-La Roche Inc. (collectively, 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 its 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 June 30, 2019, the Company has not recognized any milestone revenue under this agreement. 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. The Company recognized revenue under this agreement of $1.0 million during each of the three month periods ended June 30, 2019 and 2018, and $2.0 million during each of the six month periods ended June 30, 2019 and 2018. At June 30, 2019, $4.0 million of revenue was deferred under this agreement, all of which was current. 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. Provention In May 2018, the Company entered into a License Agreement with Provention Bio, Inc. (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 June 30, 2019, the Company has not recognized any milestone revenue under this agreement. If PRV-3279 is 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 (Provention Asset Purchase Agreement). As partial consideration for the Provention 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 PRV-031 is 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 Provention 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 Provention 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 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, which represents the relative fair value of each performance obligation. 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 under the agreements and transferred the MGD010 license and teplizumab assets to Provention during May 2018. The warrants are reported in Other assets on the consolidated balance sheet and are revalued at each reporting period based on current Black-Scholes parameters until exercised or the warrants lapse. The resulting increase or decrease is reflected in Other income (expense) on the consolidated statement of operations and comprehensive loss. During the three and six months ended June 30, 2019, the Company recorded an increase in the valuation of the warrants of $19.6 million and $20.5 million, respectively. The warrants were valued at $22.4 million and $1.9 million as of June 30, 2019 and December 31, 2018, respectively. Subsequent to June 30, 2019, the Company exercised the warrants on a cashless basis. 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 (NIAID Agreement). Under the NIAID Agreement, 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 Topic 606.

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	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 (IRC), 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 six months ended June 30, 2019, 25,722 shares of common stock were purchased under the 2016 ESPP for net proceeds to the Company of approximately $0.4 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 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 June 30, 2019, under the 2003 Plan, there were options to purchase an aggregate of 580,190 shares of common stock outstanding at a weighted average exercise price of $2.28 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 number of shares of common stock reserved for issuance under the 2013 Plan 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 six months ended June 30, 2019, the maximum number of shares of common stock authorized to be issued by the Company under the 2013 Plan was increased to 9,938,263. 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 June 30, 2019, there were options to purchase an aggregate of 6,181,599 shares of common stock outstanding at a weighted average exercise price of $24.42 per share under the 2013 Plan. The following stock-based compensation expense was recognized for the periods indicated (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Research and development $ 2,453 $ 1,989 $ 4,267 $ 3,689 General and administrative 2,431 2,174 4,416 3,906 Total stock-based compensation expense $ 4,884 $ 4,163 $ 8,683 $ 7,595 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 for options issued during the period indicated: Six Months Ended June 30, 2019 2018 Expected dividend yield 0% 0% Expected volatility 73.7% - 75.3% 67.8% - 72.2% Risk-free interest rate 1.9% - 2.6% 2.4% - 3.1% Expected term 6.25 years 6.25 years The following table summarizes stock option activity during the six months ended June 30, 2019: Shares Weighted- Weighted-Average Aggregate Outstanding, December 31, 2018 5,273,964 $ 22.23 6.8 Granted 1,796,645 21.42 Exercised (189,428) 3.25 Forfeited or expired (119,392) 23.74 Outstanding, June 30, 2019 6,761,789 22.52 7.3 $ 8,883 As of June 30, 2019: Exercisable 3,722,761 21.92 5.9 8,850 Vested and expected to vest 6,461,922 22.46 7.2 8,880 The weighted-average grant-date fair value of options granted during the six months ended June 30, 2019 and 2018 was $14.38 and $18.29, respectively. The total intrinsic value of options exercised during the six months ended June 30, 2019 and 2018 was approximately $2.6 million and $3.7 million, respectively. The total cash received for options exercised during the six months ended June 30, 2019 and 2018 was approximately $0.6 million and $0.7 million, respectively. The total fair

(Notes)

(Notes)	6 Months Ended
	Jun. 30, 2019
Subsequent Events [Abstract]
Subsequent Event	Subsequent EventOn July 9, 2019, the Company entered into a collaboration and license agreement with I-Mab Biopharma (I-Mab), a China and U.S.-based clinical-stage biopharmaceutical company, to develop and commercialize enoblituzumab. The Company will receive an upfront payment of $15.0 million in connection with the collaboration. Assuming successful development and commercialization, the Company will also be eligible to receive additional development and regulatory milestone payments of up to $135.0 million. In addition, I-Mab will pay tiered double-digit royalties (ranging from mid-teens to twenty percent) based on annual net sales in its territories.

Basis of Presentation and Sig_2

Basis of Presentation and Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited interim consolidated financial statements of MacroGenics, Inc. (the Company) have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information. The financial statements include all adjustments (consisting only of normal recurring adjustments) that the management of the Company believes are necessary for a fair presentation of the periods presented. These interim financial results are not necessarily indicative of results expected for the full fiscal year or for any subsequent interim period. The accompanying unaudited interim 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. These consolidated financial statements and related notes should be read in conjunction with the financial statements and notes thereto included in the Company's 2018 Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) on February 26, 2019.
Recently Adopted and Issued Accounting Standards	Recently Adopted Accounting Standards In February 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-02, which requires lessees to recognize a right-of-use (ROU) asset and a lease liability for all leases with terms greater than 12 months and also requires disclosures by lessees and lessors about the amount, timing and uncertainty of cash flows arising from leases. Subsequent to the issuance of ASU 2016-02, the FASB clarified the guidance through several ASUs, with the resulting guidance collectively referred to as ASC 842. The Company adopted ASC 842 effective January 1, 2019, using the optional transition method provided under ASU 2018-11, which did not require adjustments to comparative periods nor require modified disclosures in those comparative periods. The Company has elected not to recognize leases with terms of one year or less on the balance sheet. At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances. For leases where the Company is the lessee, ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent an obligation to make lease payments arising from the lease. ROU assets and lease liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. The interest rate implicit in lease contracts is typically not readily determinable. As such, the Company utilizes the appropriate incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term of the lease for which the rate is estimated. Certain adjustments to the ROU asset may be required for items such as initial direct costs paid or incentives received. The lease terms used to calculate the ROU asset and related lease liabilities include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Lease expense for operating leases is recognized on a straight-line basis over the lease term as an operating expense while the expense for finance leases is recognized as depreciation expense and interest expense using the accelerated interest method of recognition. The Company has lease agreements which require payments for lease and non-lease components and has elected the practical expedient not to separate non-lease components from lease components for all classes of underlying assets. As a result of the cumulative impact of adopting ASC 842, the Company recorded operating lease ROU assets of $16.4 million and operating lease liabilities of $27.7 million as of January 1, 2019, primarily related to real estate leases, based on the present value of the future lease payments on the date of adoption. The ROU asset is included in Other assets on the consolidated balance sheets. Refer to Note 4, Leases, for additional disclosures required by ASC 842. Recently Issued Accounting Standards 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.

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Financial Assets Measured at Fair Value on a Recurring Basis	Financial assets measured at fair value on a recurring basis were as follows (in thousands): Fair Value Measurements at June 30, 2019 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 $ 55,663 $ 55,663 $ — $ — Government-sponsored enterprises 20,927 — 20,927 — Corporate debt securities 84,356 — 84,356 — Common stock warrants 22,356 — — 22,356 Total assets measured at fair value (a) $ 183,302 $ 55,663 $ 105,283 $ 22,356 Fair Value Measurements 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 (b) $ 160,849 $ 46,257 $ 112,702 $ 1,890 (a) Total assets measured at fair value at June 30, 2019 includes approximately $69.1 million reported in cash and cash equivalents and $22.4 million reported in other assets on the balance sheet. (b) 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 and $1.9 million reported in other assets on the balance sheet.

Marketable Securities (Tables)

Marketable Securities (Tables)	6 Months Ended
	Jun. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Available-for-sale Marketable Securities	Available-for-sale marketable securities as of June 30, 2019 and December 31, 2018 were as follows (in thousands): June 30, 2019 Amortized Gross Gross Fair Government-sponsored enterprises $ 20,919 $ 8 $ — $ 20,927 Corporate debt securities 70,867 26 — 70,893 Total $ 91,786 $ 34 $ — $ 91,820 December 31, 2018 Amortized Gross Gross Fair Corporate debt securities $ 12,738 $ — $ (3) $ 12,735

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2019
Leases [Abstract]
Lease, Cost	The components of lease cost for the six months ended June 30, 2019 were as follows (in thousands): Operating lease cost $ 2,701 Variable lease cost 618 Sublease income (471) Net lease cost $ 2,848
Lessee, Operating Lease, Liability, Maturity	As of June 30, 2019, the maturities of our operating lease liabilities were as follows (in thousands): Remainder of 2019 $ 3,201 2020 5,603 2021 5,291 2022 5,450 2023 5,279 2024 4,293 Thereafter 10,081 Total lease payments 39,198 Present value adjustment (11,276) Lease liabilities $ 27,922

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation Expense	The following stock-based compensation expense was recognized for the periods indicated (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Research and development $ 2,453 $ 1,989 $ 4,267 $ 3,689 General and administrative 2,431 2,174 4,416 3,906 Total stock-based compensation expense $ 4,884 $ 4,163 $ 8,683 $ 7,595
Valuation Assumptions Using the Black-Scholes Option-Pricing Model	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 for options issued during the period indicated: Six Months Ended June 30, 2019 2018 Expected dividend yield 0% 0% Expected volatility 73.7% - 75.3% 67.8% - 72.2% Risk-free interest rate 1.9% - 2.6% 2.4% - 3.1% Expected term 6.25 years 6.25 years
Stock Option and Restricted Stock Unit Activity	The following table summarizes stock option activity during the six months ended June 30, 2019: Shares Weighted- Weighted-Average Aggregate Outstanding, December 31, 2018 5,273,964 $ 22.23 6.8 Granted 1,796,645 21.42 Exercised (189,428) 3.25 Forfeited or expired (119,392) 23.74 Outstanding, June 30, 2019 6,761,789 22.52 7.3 $ 8,883 As of June 30, 2019: Exercisable 3,722,761 21.92 5.9 8,850 Vested and expected to vest 6,461,922 22.46 7.2 8,880

Basis of Presentation and Sig_3

Basis of Presentation and Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Right-of-use asset	$ 17,100	$ 16,400
Lease liabilities	$ 27,922	$ 27,700

Fair Value of Financial Instr_3

Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Assets:
Securities	$ 91,820
Other assets	43,785	$ 6,294
Fair Value Measurements, Recurring Basis
Assets:
Cash and cash equivalents	69,100	146,200
Total assets measured at fair value	183,302	160,849
Other assets	22,400	1,900
Fair Value Measurements, Recurring Basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total assets measured at fair value	55,663	46,257
Fair Value Measurements, Recurring Basis | Significant Other Observable Inputs (Level 2)
Assets:
Total assets measured at fair value	105,283	112,702
Fair Value Measurements, Recurring Basis | Significant Unobservable Inputs (Level 3)
Assets:
Total assets measured at fair value	22,356	1,890
Fair Value Measurements, Recurring Basis | Money market funds
Assets:
Cash and cash equivalents	55,663	46,257
Fair Value Measurements, Recurring Basis | Money market funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash and cash equivalents	55,663	46,257
Fair Value Measurements, Recurring Basis | Money market funds | Significant Other Observable Inputs (Level 2)
Assets:
Cash and cash equivalents	0	0
Fair Value Measurements, Recurring Basis | Money market funds | Significant Unobservable Inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Fair Value Measurements, Recurring Basis | U.S. Treasury securities
Assets:
Securities		12,488
Fair Value Measurements, Recurring Basis | U.S. Treasury securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Securities		0
Fair Value Measurements, Recurring Basis | U.S. Treasury securities | Significant Other Observable Inputs (Level 2)
Assets:
Securities		12,488
Fair Value Measurements, Recurring Basis | U.S. Treasury securities | Significant Unobservable Inputs (Level 3)
Assets:
Securities		0
Fair Value Measurements, Recurring Basis | Government-sponsored enterprises
Assets:
Securities	20,927
Fair Value Measurements, Recurring Basis | Government-sponsored enterprises | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Securities	0
Fair Value Measurements, Recurring Basis | Government-sponsored enterprises | Significant Other Observable Inputs (Level 2)
Assets:
Securities	20,927
Fair Value Measurements, Recurring Basis | Government-sponsored enterprises | Significant Unobservable Inputs (Level 3)
Assets:
Securities	0
Fair Value Measurements, Recurring Basis | Corporate debt securities
Assets:
Securities	84,356	100,214
Fair Value Measurements, Recurring Basis | Corporate debt securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Securities	0	0
Fair Value Measurements, Recurring Basis | Corporate debt securities | Significant Other Observable Inputs (Level 2)
Assets:
Securities	84,356	100,214
Fair Value Measurements, Recurring Basis | Corporate debt securities | Significant Unobservable Inputs (Level 3)
Assets:
Securities	0	0
Fair Value Measurements, Recurring Basis | Common stock warrants
Assets:
Securities	22,356	1,890
Fair Value Measurements, Recurring Basis | Common stock warrants | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Securities	0	0
Fair Value Measurements, Recurring Basis | Common stock warrants | Significant Other Observable Inputs (Level 2)
Assets:
Securities	0	0
Fair Value Measurements, Recurring Basis | Common stock warrants | Significant Unobservable Inputs (Level 3)
Assets:
Securities	$ 22,356	$ 1,890

Marketable Securities (Details)

Marketable Securities (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 91,786,000
Gross Unrealized Gains	34,000
Gross Unrealized Losses	0
Fair Value	91,820,000
Other-than-temporary unrealized losses	0	$ 0
Government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	20,919,000
Gross Unrealized Gains	8,000
Gross Unrealized Losses	0
Fair Value	20,927,000
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	70,867,000	12,738,000
Gross Unrealized Gains	26,000	0
Gross Unrealized Losses	0	(3,000)
Fair Value	$ 70,893,000	$ 12,735,000

Leases Narrative (Details)

Leases Narrative (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
Weighted average lease term	7 years
Lease renewal term	5 years
Discount rate	9.90%
Right-of-use asset	$ 17.1	$ 16.4
Operating Lease, Payments	3.2
Operating Lease, Payments	$ 3.2
Maximum
Lessee, Lease, Description [Line Items]
Lease renewal term	14 years
Minimum
Lessee, Lease, Description [Line Items]
Lease renewal term	5 years

Lease Costs (Details)

Lease Costs (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jan. 01, 2019
Leases [Abstract]
Operating lease cost	$ 2,701
Variable Lease, Cost	618
Sublease income	(471)
Net lease cost	2,848
Remainder of 2019	3,201
2020	5,603
2021	5,291
2022	5,450
2023	5,279
2024	4,293
Thereafter	10,081
Total lease payments	39,198
Present value adjustment	(11,276)
Lease liabilities	$ 27,922	$ 27,700

Stockholders' Equity (Details)

Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		6 Months Ended
	Feb. 28, 2019	Apr. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Class of Stock [Line Items]
Proceeds from issuance of common stock, net of offering costs			$ 118,657	$ 103,259
Firm Commitment Public Underwritten Offer
Class of Stock [Line Items]
Number of shares issued or sold (in shares)		4,500,000
Common stock purchase price (in dollars per share)		$ 21.25
Proceeds from issuance of common stock, net of offering costs		$ 103,000
Over-allotment option
Class of Stock [Line Items]
Number of shares issued or sold (in shares)	825,000	675,000
Common stock purchase price (in dollars per share)	$ 20	$ 21.25
Follow-On Equity Offering
Class of Stock [Line Items]
Number of shares issued or sold (in shares)	5,500,000
Common stock purchase price (in dollars per share)	$ 20
Proceeds from issuance of common stock, net of offering costs	$ 118,700

Collaboration and Other Agree_2

Collaboration and Other Agreements - Incyte (Details) $ in Thousands	1 Months Ended	3 Months Ended			6 Months Ended		12 Months Ended
	Oct. 31, 2017USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2017USD ($)performance_obligation	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2018USD ($)
Collaboration And Other Agreements [Line Items]
Revenues		$ 10,593	$ 18,834		$ 20,255	$ 23,529
Incyte Corporation | Incyte MGA012 Agreement
Collaboration And Other Agreements [Line Items]
Non-refundable upfront payment				$ 150,000
Potential development and regulatory milestone payments under agreement	$ 420,000
Potential commercial milestone payments under agreement	330,000
Development and regulatory milestones recognized					15,000		$ 15,000
Number of performance obligations | performance_obligation				2
Collaborative agreement transaction price	154,000
Variable consideration recognized	$ 4,000
Maximum | Incyte Corporation | Incyte MGA012 Agreement
Collaboration And Other Agreements [Line Items]
Proceeds from royalties (percent)	24.00%
Minimum | Incyte Corporation | Incyte MGA012 Agreement
Collaboration And Other Agreements [Line Items]
Proceeds from royalties (percent)	15.00%
Revenues From License Agreements | Incyte Corporation | Incyte MGA012 Agreement
Collaboration And Other Agreements [Line Items]
Revenues	$ 150,000				8,200
Revenues From License Agreements | Incyte Corporation | Incyte MGA012 Agreement - Clinical activities
Collaboration And Other Agreements [Line Items]
Revenues		0	600		$ 100	3,100
Revenues From License Agreements | Incyte Corporation | Incyte MGA012 Agreement - Services
Collaboration And Other Agreements [Line Items]
Revenues		$ 4,200	$ 9,900			$ 9,900

Collaboration and Other Agree_3

Collaboration and Other Agreements - Les Laboratoires Servier (Details) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Sep. 30, 2012USD ($)exclusive_licenseperformance_obligation	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2014USD ($)componentmilestone	Dec. 31, 2018USD ($)
Collaboration And Other Agreements [Line Items]
Revenues		$ 10,593	$ 18,834	$ 20,255	$ 23,529
Deferred revenue, current		14,449		14,449			$ 21,721
Deferred revenue, net of current portion		15,413		15,413			19,001
Servier
Collaboration And Other Agreements [Line Items]
Number of performance obligations | performance_obligation	3
Number of components in license agreement | component						2
Servier | Servier DART
Collaboration And Other Agreements [Line Items]
Number of exclusive options to license | exclusive_license	3
Non-refundable upfront payment	$ 20,000
Collaborative agreement transaction price	$ 20,000
Number of milestones achieved | milestone						2
Milestone Payment						$ 5,000
Option exercise fee						$ 15,000
Offset to research and development costs under the collaboration agreement		1,200	1,600	2,000	2,800
Deferred revenue		12,100		12,100			12,600
Deferred revenue, current		1,700		1,700			900
Deferred revenue, net of current portion		10,400		10,400			$ 11,700
Revenues From License Agreements | Servier | Servier DART
Collaboration And Other Agreements [Line Items]
Revenues		300	300	500	600
Revenues From License Agreements | Les Laboratoires Servier MGD007 | Servier | Servier DART
Collaboration And Other Agreements [Line Items]
Revenues		$ 0	$ 400	$ 0	$ 900

Collaboration and Other Agree_4

Collaboration and Other Agreements - Roche (Details) $ in Thousands	1 Months Ended		3 Months Ended		6 Months Ended
	Jan. 31, 2018USD ($)	Dec. 31, 2017USD ($)performance_obligation	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2018USD ($)
Collaboration And Other Agreements [Line Items]
Revenues			$ 10,593	$ 18,834	$ 20,255	$ 23,529
Deferred revenue, current			14,449		14,449		$ 21,721
Deferred revenue, net of current portion			15,413		15,413		19,001
F. Hoffmann-La Roche Ltd. and Hoffmann-La Roche Inc.
Collaboration And Other Agreements [Line Items]
Non-refundable upfront payment	$ 10,000
Potential milestone payments and royalties on future sales under agreement		$ 370,000
Number of performance obligations | performance_obligation		1
Collaborative agreement transaction price		$ 10,000
Upfront payment recognition period		30 months
Deferred revenue							6,000
Deferred revenue, current			4,000		$ 4,000		4,000
Deferred revenue, net of current portion							$ 2,000
Revenues From License Agreements | F. Hoffmann-La Roche Ltd. and Hoffmann-La Roche Inc.
Collaboration And Other Agreements [Line Items]
Revenues			$ 1,000	$ 1,000

Collaboration and Other Agree_5

Collaboration and Other Agreements - Zai Lab (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Nov. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Collaboration And Other Agreements [Line Items]
Revenues		$ 10,593	$ 18,834	$ 20,255	$ 23,529
Deferred revenue, current		14,449		14,449		$ 21,721
Deferred revenue, net of current portion		15,413		15,413		19,001
Zai Labs Collaboration and License Agreement | Zai Labs
Collaboration And Other Agreements [Line Items]
Non-refundable upfront payment	$ 25,000
Nonrefundable payment tax withholding	$ 2,500
Potential development and regulatory milestone payments under agreement		140,000		140,000
Revenues		4,000		8,000
Deferred revenue		13,100		13,100		21,100
Deferred revenue, current		8,100		8,100		16,100
Deferred revenue, net of current portion		$ 5,000		5,000		$ 5,000
Revenues From License Agreements | Zai Labs Collaboration and License Agreement | Zai Labs
Collaboration And Other Agreements [Line Items]
Revenues				$ 2,000	$ 2,000

Collaboration and Other Agree_6

Collaboration and Other Agreements - Provention (Details)	May 31, 2018USD ($)performance_obligation$ / sharesshares	Jun. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2018USD ($)
Collaboration And Other Agreements [Line Items]
Revenues		$ 10,593,000		$ 18,834,000	$ 20,255,000	$ 23,529,000
Fair Value		91,820,000			91,820,000
Provention
Collaboration And Other Agreements [Line Items]
Number of performance obligations | performance_obligation	2
Collaborative agreement transaction price	$ 6,100,000
Number of shares available under warrants (in shares) | shares	2,432,688
License Agreement | Provention | Provention PRV-3279
Collaboration And Other Agreements [Line Items]
Warrant to purchase shares of common stock, exercise price (in dollars per share) | $ / shares	$ 2.50
Potential development and regulatory milestone payments under agreement	$ 65,000,000
Potential commercial milestone payments under agreement	$ 225,000,000
Asset Purchase Agreement | Provention | Provention PRV-031
Collaboration And Other Agreements [Line Items]
Warrant to purchase shares of common stock, exercise price (in dollars per share) | $ / shares	$ 2.50
Potential development and regulatory milestone payments under agreement	$ 170,000,000
Potential commercial milestone payments under agreement	225,000,000
Potential milestone payments to third parties	$ 1,300,000
Revenues From License Agreements | Provention
Collaboration And Other Agreements [Line Items]
Revenues			$ 6,100,000
Common stock warrants
Collaboration And Other Agreements [Line Items]
Increase in valuation		19,600,000			20,500,000
Fair Value Measurements, Recurring Basis | Common stock warrants
Collaboration And Other Agreements [Line Items]
Fair Value		$ 22,356,000			$ 22,356,000		$ 1,890,000

Collaboration and Other Agree_7

Collaboration and Other Agreements - NIAID Contract (Details)	Sep. 15, 2015USD ($)Molecule	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Collaboration And Other Agreements [Line Items]
Revenues		$ 10,593,000	$ 18,834,000		$ 20,255,000	$ 23,529,000
NIAID
Collaboration And Other Agreements [Line Items]
Commercialization of molecules | Molecule	2
Base period	$ 7,500,000
Additional development funding options under agreement	17,000,000
Total potential value	$ 24,500,000
Proceeds from additional development funding options under agreement									$ 10,800,000
Revenues From Grants | NIAID
Collaboration And Other Agreements [Line Items]
Revenues				$ 200,000	$ 600,000	$ 600,000	$ 800,000	$ 400,000

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended		9 Months Ended
	May 31, 2017	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding (in shares)		6,761,789		6,761,789				5,273,964
Weighted-average exercise price of stock options outstanding (in dollars per share)		$ 22.52		$ 22.52				$ 22.23
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense		$ 4,884	$ 4,163	$ 8,683	$ 7,595
2016 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
Payroll deduction discount	10.00%
Purchase price of common stock percent of the fair market value	85.00%
Common stock purchased (in shares)				25,722
Proceeds from ESPP						$ 400
2003 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding (in shares)		580,190		580,190
Weighted-average exercise price of stock options outstanding (in dollars per share)		$ 2.28		$ 2.28
Stock Incentive Plan 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of shares authorized (in shares)		9,938,263		9,938,263
Potential annual increase in shares reserved for future issuance (in shares)		1,960,168		1,960,168
Potential annual increase in shares reserved for future issuance as percentage of outstanding share				4.00%
Options outstanding (in shares)		6,181,599		6,181,599
Weighted-average exercise price of stock options outstanding (in dollars per share)		$ 24.42		$ 24.42
Research and Development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense				$ 2,453	1,989	4,267	$ 3,689
General and Administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense				$ 2,431	$ 2,174	$ 4,416	$ 3,906

Stock-Based Compensation - Opti

Stock-Based Compensation - Option Pricing Assumptions (Details)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%
Expected term	6 years 3 months	6 years 3 months
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	73.70%	67.80%
Risk-free interest rate	1.90%	2.40%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	75.30%	72.20%
Risk-free interest rate	2.60%	3.10%

Stock-Based Compensation - St_2

Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares, Outstanding, Beginning Balance (in shares)	5,273,964		5,273,964
Shares, Granted (in shares)			1,796,645
Shares, Exercised (in shares)			(189,428)
Shares, Forfeited or expired (in shares)			(119,392)
Shares, Outstanding, Ending Balance (in shares)			6,761,789
Shares, Exercisable (in shares)			3,722,761
Shares, Vested and expected to vest (in shares)			6,461,922
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted- Average Exercise Price, Outstanding, Beginning Balance (in dollars per share)	$ 22.23		$ 22.23
Weighted- Average Exercise Price, Granted (in dollars per share)			21.42
Weighted- Average Exercise Price, Exercised (in dollars per share)			3.25
Weighted- Average Exercise Price, Forfeited or expired (in dollars per share)			(23.74)
Weighted- Average Exercise Price, Outstanding, Ending Balance (in dollars per share)			22.52
Weighted- Average Exercise Price, Exercisable (in dollars per share)			21.92
Weighted- Average Exercise Price, Vested and expected to vest (in dollars per share)			$ 22.46
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 3 months 18 days
Weighted- Average Remaining Contractual Term, Exercisable			5 years 10 months 24 days
Weighted- Average Remaining Contractual Term, Vested and expected to vest			7 years 2 months 12 days
Aggregate Intrinsic Value, Outstanding, Ending Balance			$ 8,883
Aggregate Intrinsic Value, Exercisable			8,850
Aggregate Intrinsic Value, Vested and expected to vest			$ 8,880
Weighted-average grant-date fair value of options granted (in dollars per share)		$ 18.29	$ 14.38
Intrinsic value of options exercised		$ 3,700	$ 2,600
Cash received for options exercised		700	600
Fair value of shares vested		$ 6,300	6,500
Unrecognized compensation expense related to non-vested stock-options, net of related forfeiture estimates			$ 38,700
Unrecognized compensation expense recognition period			2 years 10 months 24 days

Subsequent Events - Narrative (

Subsequent Events - Narrative (Details) - Subsequent Event - I-Mab	Jul. 09, 2019USD ($)
Subsequent Event [Line Items]
Non-refundable upfront payment	$ 15,000,000
Potential development and regulatory milestone payments under agreement	$ 135,000,000

Uncategorized Items - mgnx-2019

Label	Element	Value
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ (6,479,000)
Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ (6,479,000)