Xencor (XNCR) 10-K 25 Feb 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2019	Feb. 14, 2020	Jun. 28, 2019
Document and Entity Information
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2019
Entity File Number	001-36182
Entity Registrant Name	Xencor, Inc
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-1622502
Entity Address, Address Line One	111 West Lemon Avenue
Entity Address, City or Town	Monrovia
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	91016
City Area Code	626
Local Phone Number	305-5900
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	XNCR
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		56,943,858
Entity Central Index Key	0001326732
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Public Float			$ 2,291,908,831
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 50,312	$ 26,246
Marketable securities	479,470	268,115
Accounts receivable	21,574	10,187
Income tax receivable	502	804
Prepaid expenses and other current assets	6,547	10,375
Total current assets	558,405	315,727
Property and equipment, net	15,805	11,813
Patents, licenses, and other intangible assets, net	14,421	11,969
Marketable securities - long term	71,526	236,108
Income tax receivable	402	804
Right-of-use assets	9,380
Other assets	311	311
Total assets	670,250	576,732
Current liabilities
Accounts payable	10,189	3,797
Accrued expenses	8,995	9,662
Deferred rent		315
Lease liabilities	2,169
Deferred revenue	45,205	40,079
Total current liabilities	66,558	53,853
Deferred rent, net of current portion		1,198
Lease liabilities, net of current portion	8,565
Deferred revenue, net of current portion	1,926
Total liabilities	77,049	55,051
Commitments and contingencies (see note 9)
Stockholders' equity
Preferred stock, $0.01 par value: 10,000,000 authorized shares; -0- issued and outstanding shares at December 31, 2019 and 2018
Common stock, $0.01 par value: 200,000,000 authorized shares; 56,902,301 issued and outstanding shares at December 31, 2019 and 56,279,542 issued and outstanding at December 31, 2018	569	563
Additional paid-in capital	887,873	845,366
Accumulated other comprehensive income (loss)	1,161	(971)
Accumulated deficit	(296,402)	(323,277)
Total stockholders' equity	593,201	521,681
Total liabilities and stockholders' equity	$ 670,250	$ 576,732

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Balance Sheets
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	56,902,301	56,279,542
Common stock, shares outstanding	56,902,301	56,279,542

Statements of Comprehensive Inc

Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue
Collaborations, licenses, milestones, and royalties	$ 156,700	$ 40,603	$ 46,150
Operating expenses
Research and development	118,590	97,501	71,772
General and administrative	24,286	22,472	17,501
Total operating expenses	142,876	119,973	89,273
Income (loss) from operations	13,824	(79,370)	(43,123)
Other income (expenses)
Interest income, net	13,619	9,086	4,181
Other income (expense)	(256)	(125)	(7)
Total other income, net	13,363	8,961	4,174
Income (loss) before income tax	27,187	(70,409)	(38,949)
Income tax expense (benefit)	312	0	(463)
Net income (loss)	26,875	(70,409)	(38,486)
Other comprehensive income (loss)
Net unrealized gain (loss) on marketable securities available-for-sale	2,132	837	(367)
Comprehensive income (loss)	$ 29,007	$ (69,572)	$ (38,853)
Net income (loss) per share attributable to common stockholders:
Basic net income (loss) (in dollars per share)	$ 0.48	$ (1.31)	$ (0.82)
Diluted net income (loss) (in dollars per share)	$ 0.46	$ (1.31)	$ (0.82)
Weighted average shares used to compute net income (loss) per share attributable to common stockholders:
Basic (in shares)	56,531,439	53,942,116	46,817,756
Diluted (in shares)	58,467,880	53,942,116	46,817,756

Statement of Stockholders' Equi

Statement of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Total
Balance at Dec. 31, 2016	$ 466	$ 553,290	$ (1,441)	$ (214,382)	$ 337,933
Balance (in shares) at Dec. 31, 2016	46,567,978
Increase (Decrease) in Stockholders' Equity
Sale of common stock, net of issuance cost	$ 4	2,793			2,797
Sale of common stock, net of issuance cost (in shares)	363,603
Issuance of common stock under the Employee Stock Purchase Plan		936			936
Issuance of common stock under the Employee Stock Purchase Plan (in shares)	70,907
Comprehensive income (loss)			(367)	(38,486)	(38,853)
Stock-based compensation expense		13,651			13,651
Balance at Dec. 31, 2017	$ 470	570,670	(1,808)	(252,868)	316,464
Balance (in shares) at Dec. 31, 2017	47,002,488
Increase (Decrease) in Stockholders' Equity
Sale of common stock, net of issuance cost	$ 84	245,420			245,504
Sale of common stock, net of issuance cost (in shares)	8,395,000
Issuance of common stock upon exercise of stock awards	$ 8	7,609			7,617
Issuance of common stock upon exercise of stock awards (in shares)	824,731
Issuance of common stock under the Employee Stock Purchase Plan	$ 1	1,119			1,120
Issuance of common stock under the Employee Stock Purchase Plan (in shares)	57,323
Comprehensive income (loss)			837	(70,409)	(69,572)
Stock-based compensation expense		20,548			20,548
Balance at Dec. 31, 2018	$ 563	845,366	(971)	(323,277)	521,681
Balance (in shares) at Dec. 31, 2018	56,279,542
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of stock awards	$ 5	9,264			9,269
Issuance of common stock upon exercise of stock awards (in shares)	543,887
Issuance of common stock under the Employee Stock Purchase Plan	$ 1	1,392			1,393
Issuance of common stock under the Employee Stock Purchase Plan (in shares)	67,561
Issuance of restricted stock units (in shares)	11,311
Comprehensive income (loss)			2,132	26,875	29,007
Stock-based compensation expense		31,851			31,851
Balance at Dec. 31, 2019	$ 569	$ 887,873	$ 1,161	$ (296,402)	$ 593,201
Balance (in shares) at Dec. 31, 2019	56,902,301

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities
Net income (loss)	$ 26,875	$ (70,409)	$ (38,486)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization	4,298	3,251	2,030
Amortization of premium on marketable securities	(4,321)	(394)	2,845
Stock-based compensation	31,851	20,548	13,651
Abandonment of capitalized intangible assets	221	239	396
Loss on disposal of assets	8	102	83
Loss on sale of marketable securities available-for-sale		74
Changes in operating assets and liabilities:
Accounts receivable	(11,321)	(9,045)	7,474
Interest receivable	(387)	(535)	(307)
Prepaid expenses and other assets	3,828	(4,769)	(2,705)
Income tax receivable	704	(84)	(1,524)
Other assets		(46)	(161)
Accounts payable	6,392	(3,072)	2,989
Accrued expenses	(667)	4,182	(1,212)
Income taxes		(157)	91
Deferred rent	(1,513)	398	589
Lease liabilities and ROU assets	1,354
Deferred revenue	7,052	(20,039)	(19,350)
Net cash provided by (used in) operating activities	64,374	(79,756)	(33,597)
Cash flows from investing activities
Proceeds from sale and maturities of marketable securities available-for-sale	456,923	222,125	115,757
Proceeds from sale of property and equipment		9
Purchase of marketable securities	(496,855)	(377,840)	(76,529)
Purchase of intangible assets	(3,685)	(1,935)	(1,967)
Purchase of property and equipment	(7,353)	(7,212)	(5,311)
Proceeds from repayment of (investment in) loan receivable		86	(86)
Net cash provided by (used in) investing activities	(50,970)	(164,767)	31,864
Cash flows from financing activities
Proceeds from issuance of common stock upon exercise of stock awards	9,269	7,617	2,797
Proceeds from issuance of common stock under the Employee Stock Purchase Plan	1,393	1,120	936
Proceeds from issuance of common stock		260,245
Common stock issuance costs		(14,741)
Net cash provided by financing activities	10,662	254,241	3,733
Net increase in cash and cash equivalents	24,066	9,718	2,000
Cash and cash equivalents, beginning of period	26,246	16,528	14,528
Cash and cash equivalents, end of period	50,312	26,246	16,528
Cash paid for:
Interest	11	16	13
Income taxes	400	233	969
Supplemental Schedule of Noncash Investing Activities
Net unrealized gain (loss) on marketable securities available-for-sale	$ 2,132	$ 837	$ (367)

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	1. Summary of Significant Accounting Policies Description of Business Xencor, Inc. (we, us, our, or the Company) was incorporated in California in 1997 and reincorporated in Delaware in September 2004. We are a clinical-stage biopharmaceutical company focused on discovering and developing engineered monoclonal antibody and proteins to treat severe and life-threatening diseases with unmet medical needs. We use our proprietary XmAb technology platform to create next-generation antibody product candidates designed to treat cancer and autoimmune diseases. We focus on the portion of the antibody that interacts with multiple segments of the immune system, referred to as the Fc domain, which is constant and interchangeable among antibodies. Our engineered Fc domains, the XmAb technology, are applied to our pipeline of antibody and protein-based drug candidates to increase immune inhibition, improve cytotoxicity, extend half-life and most recently to create bispecific antibodies and cytokines. Our operations are based in Monrovia, California and San Diego, California. Basis of Presentation The Company’s financial statements as of December 31, 2019, 2018, and 2017 and for the years then ended have been prepared in accordance with accounting principles generally accepted in the United States (U.S.). Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Significant estimates include useful lives of long-lived assets, the periods over which certain revenues and expenses will be recognized including collaboration revenue recognized from non-refundable upfront licensing payments, the amount of non-cash compensation costs related to share-based payments to employees and non-employees and the period over which these costs are expensed. Recent Accounting Pronouncements Pronouncements adopted in 2019 Pronouncements not yet effective In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments Codification Improvements to Topic 326, Financial Instruments – Credit Losses In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement In August 2018, the FASB issued ASU No. 2018-15, Intangibles – Goodwill and Other – Internal Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract In October 2018, the FASB issued ASU No. 2018-17, Consolidation (Topic 810): Targeted Improvements to Related Party Guidance for Variable Interest Entities In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction Between Topic 808 and Topic 606 In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes Revenue Recognition We have, to date, earned revenue from research and development collaborations, which may include research and development services, licenses of our internally developed technologies, licenses of our internally developed drug candidates, or combinations of these. The terms of our license and research and development and collaboration agreements generally include non-refundable upfront payments, research funding, co-development reimbursements, license fees and, milestone and other contingent payments to us for the achievement of defined collaboration objectives and certain clinical, regulatory and sales-based events, as well as royalties on sales of any commercialized products. The terms of our licensing agreements include non-refundable upfront fees, annual licensing fees, and contractual payment obligations for the achievement of pre-defined preclinical, clinical, regulatory and sales-based events by our partners. The licensing agreements also include royalties on sales of any commercialized products by our partners. We recognize revenue through the five-step process in accordance with ASC 606 Revenue Recognition when control of the promised goods or services is transferred to our customers in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. Deferred Revenue Deferred revenue arises from payments received in advance of the culmination of the earnings process. We have classified deferred revenue for which we stand ready to perform within the next 12 months as a current liability. We recognize deferred revenue as revenue in future periods when the applicable revenue recognition criteria have been met. The total amounts reported as deferred revenue were $47.1 million and $40.1 million at December 31, 2019 and 2018, respectively. Research and Development Expenses Research and development expenses include costs we incur for our own and for our collaborators’ research and development activities. Research and development costs are expensed as incurred. These costs consist primarily of salaries and benefits, including associated stock-based compensation, laboratory supplies, facility costs, and applicable overhead expenses of personnel directly involved in the research and development of new technology and products, as well as fees paid to other entities that conduct certain research development activities on our behalf. We estimate preclinical study and clinical trial expenses based on the services performed pursuant to the contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and clinical trials on our behalf based on the actual time and expenses incurred by them. Further, we accrue expenses related to clinical trials based on the level of patient enrollment and activity according to the related agreement. We monitor patient enrollment levels and related activity to the extent reasonably possible and adjust estimates accordingly. We capitalize acquired research and development technology licenses and third-party contract rights and amortize the costs over the shorter of the license term or the expected useful life. We review the license arrangements and the amortization period on a regular basis and adjust the carrying value or the amortization period of the licensed rights if there is evidence of a change in the carrying value or useful life of the asset. Cash and Cash Equivalents We consider cash equivalents to be only those investments which are highly liquid, readily convertible to cash and which mature within three months from the date of purchase. Marketable Securities The Company has an investment policy that includes guidelines on acceptable investment securities, minimum credit quality, maturity parameters and concentration and diversification. The Company invests its excess cash primarily in marketable debt securities issued by investment grade institutions. The Company considers its marketable debt securities to be “available-for-sale”, as defined by authoritative guidance issued by the FASB. These assets are carried at fair value and the unrealized gains and losses are included in accumulated other comprehensive income (loss). Accrued interest on marketable debt securities is included in marketable securities. Accrued interest was $2.7 million and $2.3 million at December 31, 2019 and 2018, respectively. If a decline in the value of a marketable security in the Company’s investment portfolio is deemed to be other-than-temporary, the Company writes down the security to its current fair value and recognizes a loss as a charge against income. The Company reviews its portfolio of marketable debt securities, using both quantitative and qualitative factors, to determine if declines in fair value below cost are other-than-temporary. Concentrations of Risk Cash, cash equivalents and marketable debt securities are financial instruments that potentially subject the Company to concentrations of risk. We invest our cash in corporate debt securities and U.S. sponsored agencies with strong credit ratings. We have established guidelines relative to diversification and maturities that are designed to help ensure safety and liquidity. These guidelines are periodically reviewed to take advantage of trends in yields and interest rates. Cash and cash equivalents are maintained at financial institutions and, at times, balances may exceed federally insured limits. We have never experienced any losses related to these balances. Amounts on deposit in excess of federally insured limits at December 31, 2019 and 2018 approximated $50.0 million and $26.0 million, respectively. We have payables with two service providers that represent 48% of our total payables and four service providers that represented 49% of our total payables at December 31, 2019 and 2018, respectively. We rely on three critical suppliers for the manufacture of our drug product for use in our clinical trials. While we believe that there are alternative vendors available, a change in manufacturing vendors could cause a delay in the availability of drug product and result in a delay of conducting and completing our clinical trials. No other vendor accounted for more than 10% of total payables at December 31, 2019 or 2018. Fair Value of Financial Instruments Our financial instruments primarily consist of cash and cash equivalents, marketable debt securities, accounts receivable, accounts payable and accrued expenses. Marketable debt securities and cash equivalents are carried at fair value. The fair value of the other financial instruments closely approximate their fair value due to their short maturities. The Company accounts for recurring and non-recurring fair value measurements in accordance with FASB Accounting Standards Codification (ASC) 820, Fair Value Measurements and Disclosures Level 1— Level 2— Level 3— The Company measures the fair value of financial assets using the highest level of inputs that are reasonably available as of the measurement date. The assets recorded at fair value are classified within the hierarchy as follows for the periods reported (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ Total ​ ​ ​ ​ ​ ​ Fair Value ​ Level 1 ​ Level 2 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money Market Funds in Cash and Cash Equivalents ​ $ 32,009 ​ $ 32,009 ​ $ — Corporate Securities ​ ​ 281,751 ​ ​ — ​ ​ 281,751 Government Securities ​ ​ 269,245 ​ ​ — ​ ​ 269,245 ​ ​ $ 583,005 ​ $ 32,009 ​ $ 550,996 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2018 ​ Total ​ ​ ​ ​ ​ ​ Fair Value ​ Level 1 ​ Level 2 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money Market Funds in Cash and Cash Equivalents ​ $ 18,270 ​ $ 18,270 ​ $ — Corporate Securities ​ ​ 104,967 ​ ​ — ​ ​ 104,967 Government Securities ​ ​ 399,256 ​ ​ — ​ ​ 399,256 ​ ​ $ 522,493 ​ $ 18,270 ​ $ 504,223 ​ Property and Equipment Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the assets. Expenditures for repairs and maintenance are charged to expense as incurred while renewals and improvements are capitalized. Useful lives by asset category are as follows: ​ ​ ​ ​ ​ ​ ​ Computers, software and equipment 3 - 5 years ​ Furniture and fixtures 5 - 7 years ​ Leasehold improvements 5 - 7 years or remaining ​ ​ ​ lease term, whichever is less ​ ​ Patents, Licenses, and Other Intangible Assets The cost of acquiring licenses is capitalized and amortized on the straight-line basis over the shorter of the term of the license or its estimated economic life, ranging from five 13 The carrying amount and accumulated amortization of patents, licenses, and other intangibles is as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2019 ​ 2018 Patents, definite life $ 10,597 $ 9,320 ​ Patents, pending issuance ​ ​ 7,266 ​ 5,644 ​ Licenses and other amortizable intangible assets ​ ​ 2,510 ​ 2,011 ​ Nonamortizable intangible assets (trademarks) ​ ​ 399 ​ 399 ​ Total gross carrying amount ​ ​ 20,772 ​ 17,374 ​ Accumulated amortization—patents ​ ​ (4,912) ​ (4,142) ​ Accumulated amortization—licenses and other ​ ​ (1,439) ​ (1,263) ​ Total intangible assets, net ​ $ 14,421 ​ $ 11,969 ​ ​ Amortization expense for patents, licenses, and other intangible assets was $0.9 million, $0.9 million and $0.8 million for the years ended December 31, 2019, 2018 and 2017, respectively. Future amortization expense for patent, licenses, and other intangible assets recorded as of December 31, 2019, and for which amortization has commenced, is as follows: ​ ​ ​ ​ ​ ​ ​ Year ended ​ ​ December 31, ​ ​ (in thousands) 2020 ​ $ 1,009 ​ 2021 ​ ​ 912 ​ 2022 ​ ​ 880 ​ 2023 ​ ​ 809 ​ 2024 ​ ​ 647 ​ Thereafter ​ ​ 2,365 ​ Total ​ $ 6,622 ​ ​ The above amortization expense forecast is an estimate. Actual amounts of amortization expense may differ from estimated amounts due to additional intangible asset acquisitions, impairment of intangible assets, accelerated amortization of intangible assets, and other events. As of December 31, 2019, the Company has $7.3 million of intangible assets which are in-process and have not been placed in service, and accordingly amortization on these assets has not commenced. Long-Lived Assets Management reviews long-lived assets which include fixed assets and amortizable intangibles for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset (or asset group) may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds the fair value of the assets. We did not recognize a loss from impairment for the years ended December 31, 2019, 2018 or 2017. Income Taxes We account for income taxes in accordance with accounting guidance which requires an asset and liability approach to financial accounting and reporting for income taxes. Deferred income tax assets and liabilities are computed annually for differences between the financial statement and tax bases of assets and liabilities that will result in taxable or deductible amounts in the future based on enacted tax laws and rates applicable to the periods in which the differences are expected to affect taxable income. Valuation allowances are established when necessary to reduce deferred tax assets to the amount expected to be realized. Income tax expense is the tax payable or refundable for the period plus or minus the change during the period in deferred tax assets and liabilities. We assess our income tax positions and record tax benefits for all years subject to examination based upon our evaluation of the facts, circumstances and information available at the reporting date. For those tax positions where there is greater than 50% likelihood that a tax benefit will be sustained, we have recorded the largest amount of tax benefit that may potentially be realized upon ultimate settlement with a taxing authority that has full knowledge of all relevant information. For those income tax positions where there is a 50% or less likelihood that a tax benefit will be sustained, no tax benefit has been recognized in the financial statements. We did not have any material uncertain tax positions at December 31, 2019 or 2018. Our policy is to recognize interest and penalties on taxes, if any, as a component of income tax expense. The Tax Cuts and Jobs Act of 2017 (TCJA) was enacted on December 22, 2017 and has several key provisions impacting the accounting for and reporting of income taxes. The most significant provisions reduced the U.S. corporate statutory tax rate from 35% to 21%, eliminated the corporate Alternative Minimum Tax (AMT) system, and made changes to the utilization and carryforward of net operating losses beginning on January 1, 2018. The tax reform provided for a refund of unused AMT carryforwards for years beginning after December 31, 2017. We recorded an income tax receivable as of December 31, 2019 and 2018 of $0.8 million and $1.6 million, respectively related to federal AMT carryforwards. Stock-Based Compensation We recognize compensation expense using a fair-value-based method for costs related to all share-based payments, including stock options and shares issued under our Employee Stock Purchase Plan (ESPP). Stock-based compensation cost related to employees and directors is measured at the grant date, based on the fair-value-based measurement of the award using the Black-Scholes method, and is recognized as expense over the requisite service period on a straight-line basis. We account for forfeitures when they occur. We recorded stock-based compensation and expense for stock-based awards to employees, directors and consultants of approximately $31.9 million, $20.5 million and $13.7 million for the years ended December 31, 2019, 2018 and 2017 respectively. Included in the 2019, 2018, and 2017 balances for total compensation expense is $0.7 million, $0.7 million and $0.5 million, respectively, relating to our ESPP. Options granted to individual service providers that are not employees or directors are accounted for at estimated fair value using the Black-Scholes option-pricing method and are subject to periodic re-measurement over the period during which the services are rendered. Net Income (Loss) Per Share Basic net income (loss) per common share is computed by dividing the net income or loss by the weighted-average number of common shares outstanding during the period. Potentially dilutive securities were included in the diluted net income per common share calculation for 2019. We included 1,923,310 options to purchase shares of common stock and 13,131 shares of restricted stock units (RSUs) in the calculation of the weighted-average common shares outstanding used in computing diluted net income per common share. We excluded 1,022,623 shares of options and RSUs from the calculation for 2019 because the inclusion of such shares would have had an antidilutive effect. ​ In 2018 and 2017, we excluded all options and awards from the calculations because we reported net losses in the periods and the inclusion of such shares would have had an antidilutive effect. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ 2019 ​ 2018 ​ 2017 ​ ​ (in thousands, except share and per share data) Basic ​ ​ ​ ​ Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) attributable to common stockholders for basic net income (loss) per share ​ $ 26,875 ​ $ (70,409) ​ $ (38,486) ​ Denominator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average common shares outstanding ​ ​ 56,531,439 ​ 53,942,116 ​ 46,817,756 ​ Basic net income (loss) per common share ​ $ 0.48 ​ $ (1.31) ​ $ (0.82) ​ Diluted ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) attributable to common stockholders for diluted net income (loss) per share ​ $ 26,875 ​ $ (70,409) ​ $ (38,486) ​ Denominator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average number of common shares outstanding used in computing basic net income (loss) per common share ​ ​ 56,531,439 ​ 53,942,116 ​ 46,817,756 ​ Dilutive effect of employee stock options and ESPP ​ ​ 1,936,441 ​ — ​ — ​ Weighted-average number of common shares outstanding used in computing diluted net income (loss) per common share ​ ​ 58,467,880 ​ 53,942,116 ​ 46,817,756 ​ Diluted net income (loss) per common share ​ $ 0.46 ​ $ (1.31) ​ $ (0.82) ​ ​ Segment Reporting The Company determines its segment reporting based upon the way the business is organized for making operating decisions and assessing performance. The Company has only one operating segment related to the development of pharmaceutical products .

Comprehensive Income (Loss)

Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2019
Comprehensive Income (Loss)
Comprehensive Income (Loss)	2. Comprehensive Income (Loss) Comprehensive income (loss) is comprised of net income (loss) and other comprehensive income (loss). For the years ended December 31, 2019 and 2018, the only component of other comprehensive income (loss) is net unrealized gains on marketable debt securities. There were no material reclassifications out of accumulated other comprehensive loss during the year ended December 31, 2019.

Marketable Securities

Marketable Securities	12 Months Ended
	Dec. 31, 2019
Marketable Securities
Marketable Securities	​ ​ 3. Marketable Securities The Company’s marketable debt securities held as of December 31, 2019 and 2018 are summarized below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ Amortized Unrealized ​ Unrealized ​ ​ ​ Cost ​ Gains ​ Losses ​ Fair Value (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money Market Funds ​ $ 32,009 ​ $ — ​ $ — ​ $ 32,009 Corporate Securities ​ ​ 281,586 ​ ​ 195 ​ ​ (30) ​ ​ 281,751 Government Securities ​ ​ 268,239 ​ ​ 1,006 ​ ​ — ​ ​ 269,245 ​ ​ $ 581,834 ​ $ 1,201 ​ $ (30) ​ $ 583,005 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Reported as ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 32,009 Marketable securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 550,996 Total investments ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 583,005 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2018 ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ Amortized Unrealized ​ Unrealized ​ ​ ​ Cost ​ Gains ​ Losses ​ Fair Value (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money Market Funds ​ $ 18,270 ​ $ — ​ $ — ​ $ 18,270 Corporate Securities ​ ​ 105,311 ​ ​ 1 ​ ​ (345) ​ ​ 104,967 Government Securities ​ ​ 399,873 ​ ​ 187 ​ ​ (804) ​ ​ 399,256 ​ ​ $ 523,454 ​ $ 188 ​ $ (1,149) ​ $ 522,493 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Reported as ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 18,270 Marketable securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 504,223 Total investments ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 522,493 ​ The maturities of the Company’s marketable debt securities as of December 31, 2019 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amortized Estimated ​ ​ Cost ​ Fair Value (in thousands) ​ ​ ​ ​ ​ ​ Mature in one year or less ​ $ 478,338 ​ $ 479,470 Mature after one year through five years ​ ​ 71,487 ​ ​ 71,526 ​ ​ $ 549,825 ​ $ 550,996 ​ The unrealized losses on available-for-sale investments and their related fair values as of December 31, 2019 and 2018 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ ​ Less than 12 months ​ 12 months or greater ​ ​ ​ Fair value ​ ​ Unrealized losses ​ ​ Fair value ​ ​ Unrealized gain (losses) (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate Securities ​ $ 46,303 ​ $ (24) ​ $ 13,992 ​ $ (6) Government Securities ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ $ 46,303 ​ $ (24) ​ $ 13,992 ​ $ (6) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2018 ​ ​ Less than 12 months ​ 12 months or greater ​ ​ ​ Fair value ​ ​ Unrealized losses ​ ​ Fair value ​ ​ Unrealized losses (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate Securities ​ $ 84,666 ​ $ (310) ​ $ 17,805 ​ $ (35) Government Securities ​ ​ 176,225 ​ ​ (672) ​ ​ 116,830 ​ ​ (132) ​ ​ $ 260,891 ​ $ (982) ​ $ 134,635 ​ $ (167) ​ The unrealized losses from the listed securities are due to a change in the interest rate environment and not a change in the credit quality of the securities.

Sale of Additional Common Stock

Sale of Additional Common Stock	12 Months Ended
	Dec. 31, 2019
Sale of Additional Common Stock
Sale of Additional Common Stock	4. Sale of Additional Common Stock In March 2018, we completed the sale of 8,395,000 shares of commons stock which included shares we issued pursuant to our underwriters’ exercise of their over-allotment option pursuant to a follow-on financing. We received net proceeds of $245.5 million, after underwriters’ discounts and offering expenses. On September 19, 2016, we entered into an Equity Distribution Agreement (the Distribution Agreement) with Piper Jaffray & Co (Piper Jaffray) pursuant to which we could sell from time to time, at our option, up to an aggregate of $40.0 million of common stock through Piper Jaffray as sales agent. We did not sell any shares under the Distribution Agreement, and the Distribution Agreement terminated in October 2019.

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2019
Property and Equipment
Property and Equipment	5. Property and Equipment Property and equipment consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2019 ​ 2018 ​ ​ (in thousands) Computers, software and equipment $ 21,087 $ 16,292 ​ Furniture and fixtures ​ ​ 492 ​ 173 ​ Leasehold and tenant improvements ​ ​ 6,831 ​ 4,774 ​ ​ ​ ​ 28,410 ​ 21,239 ​ Less accumulated depreciation and amortization ​ (12,605) ​ (9,426) ​ ​ ​ $ 15,805 ​ $ 11,813 ​ ​ Depreciation and amortization expense related to property and equipment in 2019, 2018 and 2017 was $3.4 million, $2.4 million and $1.2 million, respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Taxes
Income Taxes	6. Inc ome Taxes Our effective tax rate differs from the statutory federal income tax rate, primarily as a result of the changes in valuation allowance. The provision for income taxes for the year ended December 31, 2019 was $0.3 million. There was no tax provision for the year ended December 31, 2018, and the provision for income taxes for the year ended December 31, 2017 was a benefit of $0.5 million. Current tax expense of $0.3 million for the year ended December 31, 2019 represents state alternative minimum tax. A reconciliation of the federal statutory income tax to our effective income tax is as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2019 ​ 2018 ​ 2017 Federal statutory income tax $ 5,709 $ (14,795) $ (13,243) ​ State and local income taxes ​ ​ 2,549 ​ (4,767) ​ (1,806) ​ Research and development credit ​ (6,747) ​ (6,170) ​ (5,554) ​ Stock based compensation ​ ​ 1,927 ​ ​ 444 ​ ​ 2,709 ​ Effect of the 2017 Tax Cut and Jobs Act ​ ​ — ​ ​ — ​ ​ 19,596 ​ State credit ​ ​ 1,725 ​ ​ — ​ ​ — ​ Other ​ ​ (301) ​ 414 ​ 720 ​ Net change in valuation allowance ​ ​ (4,550) ​ 24,874 ​ (2,885) ​ Income tax provision (benefit) ​ $ 312 ​ $ — ​ $ (463) ​ The tax effect of temporary differences that give rise to a significant portion of the deferred tax assets and liabilities at December 31, 2019 and 2018 is presented below (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2019 2018 ​ Deferred income tax assets ​ ​ ​ ​ ​ ​ ​ Net operating loss carryforwards ​ $ 36,891 ​ $ 49,889 ​ Research credits ​ ​ 28,415 ​ 23,151 ​ Depreciation ​ ​ 334 ​ 207 ​ Unrealized loss on securities ​ ​ — ​ 269 ​ Accrued compensation ​ ​ 4,788 ​ 1,097 ​ Deferred revenue ​ ​ 11,215 ​ 11,222 ​ State taxes ​ ​ 64 ​ — ​ Gross deferred income tax assets ​ ​ 81,707 ​ 85,835 ​ Valuation allowance ​ (77,389) ​ (82,537) ​ Net deferred income tax assets ​ ​ 4,318 ​ 3,298 ​ Deferred income tax liabilities ​ ​ ​ ​ ​ ​ ​ Patent costs ​ (3,736) ​ (3,142) ​ Licensing costs ​ (229) ​ (125) ​ Capitalized legal costs ​ (26) ​ (31) ​ Unrealized gain on securities ​ ​ (327) ​ ​ — ​ Gross deferred income tax liabilities ​ (4,318) ​ (3,298) ​ Net deferred income tax asset ​ $ — ​ $ — ​ The Tax Cuts and Jobs Act of 2017 (TCJA) was enacted in December 2017 and made substantial changes in the U.S. tax system. One of the changes was elimination of the AMT tax system for corporations and allowance of an income tax refund for AMT tax credit carryforwards as of December 31, 2017. We have reported an income tax receivable of $0.8 million and $1.6 million as of December 31, 2019 and 2018 to reflect the U.S. AMT credit carryforwards we have available, which do not expire. Due to the uncertainty surrounding the realization of the benefits of our deferred tax assets in future tax periods, we have placed a valuation allowance against our deferred tax assets at December 31, 2019 and 2018. The Company recognizes valuation allowances to reduce deferred tax assets to the amount that is more likely than not to be realized. The Company’s net deferred income tax asset is not more likely than not to be realized due to the lack of sufficient sources of future taxable income and cumulative losses that have resulted over the years. During the year ended December 31, 2019, the valuation allowance decreased by $5.1 million. Upon analysis, we determined that we experienced an ownership change under Section 382 of the Internal Revenue Code and related state provisions as a result of our sale of preferred stock and sale of common stock during 2013. Sections 382 and 383 of the Internal Revenue Code limit the amount of net operating losses and tax credit forwards that may be available after a change in ownership. The Company has adjusted its net operating loss and tax credit carryforwards to reflect the impact of the limitation under sections 382 and section 383 of the Internal Revenue Code. The Company’s tax returns remain open to potential inspection for the years 2015 and onwards for federal purposes and 2014 and onwards for state purposes. As of December 31, 2019, we had cumulative net operating loss carryforwards for federal and state income tax purposes of $144.7 million and $92.8 million respectively, and available tax credit carryforwards of approximately $19.7 million for federal income tax purposes and $11.0 million for state income tax purposes, which can be carried forward to offset future taxable income, if any. The federal net operating loss carryforwards consists of $68.0 million of losses incurred prior to January 1, 2018 and which can be used to offset 100% of future taxable income and $76.7 million of losses incurred after January 1, 2018 which can be used to offset up to 80% of taxable income in subsequent years. Our federal net operating loss carryforwards expire starting in 2026, state net operating losses expire starting in 2032, and federal tax credit carryforwards began to expire starting in 2019. A total of $0.03 million in federal tax credits expired in 2019 and an additional $0.3 million will expire over the next five years if not utilized. Utilization of our net operating loss and tax credit carryforwards are subject to a substantial annual limitation under Section 382 of the Code due to the fact that we have experienced ownership changes. As a result of these changes, certain of our net operating loss and tax credit carryforwards may expire before we can use them.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2019
Stock-Based Compensation
Stock-Based Compensation	7. Stock-Based Compensation Our Board of Directors and the requisite stockholders previously approved the 2010 Equity Incentive Plan (the 2010 Plan). In October 2013, our Board of Directors approved the 2013 Equity Incentive Plan (the 2013 Plan) and in November 2013 our stockholders approved the 2013 Plan. The 2013 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance stock awards, performance cash awards, and other stock awards. The 2013 Plan became effective as of December 2, 2013, the date of the pricing of the Company’s initial public offering. As of December 2, 2013, we suspended the 2010 Plan and no additional awards may be granted under the 2010 Plan. Any shares of common stock covered by awards granted under the 2010 Plan that terminate after December 2, 2013 by expiration, forfeiture, cancellation or other means without the issuance of such shares will be added to the 2013 Plan reserve. As of December 31, 2019, the total number of shares of common stock available for issuance under the 2013 Plan was 11,277,816. Unless otherwise determined by the Board, beginning January 1, 2014, and continuing until the expiration of the 2013 Plan, the total number of shares of common stock available for issuance under the 2013 Plan will automatically increase annually on January 1 by 4% of the total number of issued and outstanding shares of common stock as of December 31 of the immediate preceding year. On January 1, 2019, the total number of shares of common stock available for issuance under the 2013 Plan was automatically increased by 2,251,181 shares, which number is included in the number of shares available for issuance above. As of December 31, 2019, a total of 8,893,515 options have been granted under the 2013 Plan. As of December 31, 2019, the Company has awarded 105,499 RSUs to certain employees pursuant to the 2013 Plan. Vesting of these awards will be in three equal annual installments and is contingent on continued employment terms. The fair value of these awards is determined based on the intrinsic value of the stock on the date of grant and will be recognized as stock-based compensation expense over the requisite service period. In November 2013, our Board of Directors and stockholders approved the 2013 Employee Stock Purchase Plan (ESPP), which became effective as of December 5, 2013. Under the ESPP our employees may elect to have between 1-15% of their compensation withheld to purchase shares of the Company’s common stock at a discount. The ESPP had an initial two-year term that includes four six-month purchase periods and employee withholding amounts may be used to purchase Company stock during each six-month purchase period. The initial two-year term ended in December 2015 and pursuant to the provisions of the ESPP, the second two-year term began automatically upon the end of the initial term. The total number of shares that can be purchased with the withholding amounts are based on the lower of 85% of the Company’s common stock price at the initial offering date or 85% of the Company’s stock price at each purchase date. We have reserved a total of 581,286 shares of common stock for issuance under the ESPP. Unless otherwise determined by our Board, beginning on January 1, 2014, and continuing until the expiration of the ESPP, the total number shares of common stock available for issuance under the ESPP will automatically increase annually on January 1 by the lesser of (i) 1% of the total number of issued and outstanding shares of common stock as of December 31 of the immediately preceding year, or (ii) 621,814 shares of common stock. On January 1, 2014, the total number of shares of common stock available for issuance under the ESPP was automatically increased by 313,545 shares, which number is included in the number of shares reserved for issuance above. Pursuant to approval by our board, there were no increases in the number of authorized shares in the ESPP in years from 2015 to 2019. As of December 31, 2019, we have issued a total of 417,277 shares of common stock under the ESPP. Total employee, director and non-employee stock-based compensation expense recognized was as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, (in thousands) ​ 2019 ​ 2018 ​ 2017 General and administrative $ 8,854 $ 7,699 $ 5,617 ​ Research and development ​ ​ 22,997 ​ 12,849 ​ 8,034 ​ ​ ​ $ 31,851 ​ $ 20,548 ​ $ 13,651 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ ​ December 31, ​ (in thousands) ​ 2019 ​ 2018 ​ 2017 ​ Stock options $ 30,502 $ 19,537 $ 13,153 ​ ESPP ​ ​ 687 ​ 744 ​ 498 ​ RSUs ​ ​ 662 ​ 267 ​ — ​ ​ ​ $ 31,851 ​ $ 20,548 ​ $ 13,651 ​ Information with respect to stock options outstanding is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2019 ​ 2018 ​ 2017 Exercisable options ​ 3,950,965 ​ 3,058,659 ​ 2,558,941 ​ Weighted average exercise price per share of exercisable options ​ $ 17.79 ​ $ 15.12 ​ $ 11.06 ​ Weighted average grant date fair value per share of options granted during the year ​ $ 20.74 ​ $ 18.06 ​ $ 16.92 ​ Options available for future grants ​ 3,975,160 ​ 3,576,574 ​ 3,394,691 ​ Weighted average remaining contractual life ​ 7.32 ​ 7.51 ​ 7.62 ​ The following table summarizes stock option activity for the years ended December 31, 2019 and 2018: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted- ​ ​ ​ ​ ​ ​ Weighted- ​ Average ​ ​ ​ ​ ​ ​ ​ Average ​ Remaining ​ ​ ​ ​ ​ ​ ​ Exercise ​ Contractual ​ Aggregate ​ ​ Number of ​ Price ​ Term ​ Intrinsic Value ​ ​ Shares ​ (Per Share) (1) ​ (in years) ​ (in thousands) (2) Balances at December 31, 2017 5,093,442 ​ 15.32 7.62 ​ $ 35,495 ​ Options granted 1,805,937 ​ ​ 27.43 ​ ​ ​ ​ ​ ​ Options forfeited (107,720) ​ ​ 21.66 ​ ​ ​ ​ ​ ​ Options exercised(3) (824,731) ​ ​ 9.24 ​ ​ ​ ​ ​ ​ Balances at December 31, 2018 5,966,928 ​ 19.71 7.51 ​ $ 99,273 ​ Options granted 2,142,228 ​ ​ 35.80 ​ ​ ​ ​ ​ ​ Options forfeited (390,950) ​ ​ 32.23 ​ ​ ​ ​ ​ ​ Options exercised(3) (543,887) ​ ​ 17.04 ​ ​ ​ ​ ​ ​ Balances at December 31, 2019 7,174,319 ​ $ 24.03 ​ 7.32 ​ $ 79,116 ​ As of December 31, 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options vested and expected to vest 7,174,319 ​ $ 24.03 7.32 ​ $ 79,116 ​ Exercisable 3,950,965 ​ $ 17.79 6.17 ​ $ 66,286 ​ (1) The weighted average exercise price per share is determined using exercise price per share for stock options. (2) The aggregate intrinsic value is calculated as the difference between the exercise price of the option and the fair value of our common stock for in-the-money options at December 31, 2019 and 2018. (3) The total intrinsic value of stock options exercised was $11.5 million, $23.6 million and $5.7 million for the years ended December 31, 2019, 2018 and 2017 respectively. The stock options outstanding and exercisable by exercise price at December 31, 2019 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock Options Outstanding ​ Stock Options Exercisable ​ ​ ​ ​ Weighted- ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Remaining Weighted- ​ Weighted- Range of ​ ​ ​ Contractual ​ Average ​ ​ ​ Average Exercise ​ Number of ​ Term ​ Exercise Price ​ Number of ​ Exercise Price Prices ​ Shares ​ (in years) ​ Per Share ​ Shares ​ Per Share $0.59 – $4.25 238,621 3.45 ​ $ 3.49 238,621 ​ $ 3.49 ​ $10.28 – $15.51 1,378,151 5.37 ​ $ 12.21 1,350,781 ​ $ 12.19 ​ $15.69 – $23.75 2,878,221 7.04 ​ $ 21.37 1,963,376 ​ $ 20.62 ​ $23.80 – $35.80 ​ 1,071,704 ​ 8.66 ​ $ 31.18 ​ 276,042 ​ $ 27.64 ​ $36.03 – $44.19 ​ 1,607,622 ​ 9.16 ​ $ 37.22 ​ 122,145 ​ $ 39.85 ​ ​ 7,174,319 7.32 ​ $ 24.03 3,950,965 ​ $ 17.79 ​ We estimated the fair value of employee and non-employee awards using the Black-Scholes valuation model. The fair value of employee stock options is being amortized on a straight-line basis over the requisite service period of the awards. Management estimates the probability of non-employee awards being vested based upon an evaluation of the non-employee achieving their specific performance goals. Options granted after our initial public offering are issued at the fair market value of our stock on the date of grant. The fair value of employee stock options was estimated using the following weighted average assumptions for the years ended December 31, 2019, 2018 and 2017: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options ​ ​ 2019 2018 2017 Common stock fair value per share ​ $ 17.37 - 25.14 ​ $ 21.80 - 43.16 ​ $ 19.61 - 25.67 ​ Expected volatility ​ 60.67% - 61.33% ​ 70.97% - 73.10% ​ 77.42% - 96.73% ​ Risk-free interest rate ​ 1.37% - 2.60% ​ 2.29% - 3.10% ​ 0.96% - 2.37% ​ Expected dividend yield ​ — ​ — ​ — ​ Expected term (in years) ​ 5.23 - 6.59 ​ 5.23 - 6.08 ​ 5.23 - 6.08 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ESPP ​ ​ 2019 2018 2017 ​ Expected term (years) 0.5 - 2.0 0.5 - 2.0 0.5 - 2.0 ​ Expected volatility ​ 50.77% - 71.37% ​ 57.04% - 71.37% ​ 67.83% - 79.76% ​ Risk-free interest rate 1.47% - 2.70% ​ 1.47% - 2.70% ​ 0.47% - 1.80% ​ Expected dividend yield ​ — ​ — ​ — ​ The expected term of stock options represents the average period the stock options are expected to remain outstanding. The expected stock price volatility for our stock options for the year ended December 31, 2019 was determined using a blended volatility by examining the historical volatility for industry peer companies and the volatility of our stock from the effective date that our shares were publicly traded on a national stock exchange. For years ended December 31, 2018 and 2017 expected stock volatility was determined by examining the historical volatilities for industry peers and adjusting for differences in our life cycle and financing leverage. Industry peers consist of several public companies in the biopharmaceutical industry. We determined the average expected life of stock options based on the simplified method because our common stock has not been publicly traded for an extended period, and we do not have a track record of our stock being traded on the public markets for sufficient time to establish the volatility of our stock. The risk-free interest rate assumption is based on the U.S. Treasury instruments whose term was consistent with the expected term of our stock options. The expected dividend assumption is based on our history and expectation of dividend payouts. The following table summarizes RSU activity for the years ended December 31, 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted- ​ ​ ​ ​ Average ​ ​ ​ ​ Grant Date ​ ​ Number of ​ Fair Value ​ ​ Shares ​ (Per Unit) Unvested at December 31, 2018 33,933 ​ $ 27.64 Granted 71,566 ​ ​ 36.68 Vested (11,311) ​ ​ 27.64 Forfeited ​ (4,182) ​ ​ 31.12 Unvested at December 31, 2019 90,006 ​ $ 34.66 As of December 31, 2019 and 2018, the unamortized compensation expense related to unvested stock options was $51.1 million and $42.8 million, respectively. The remaining unamortized compensation expense will be recognized over the next 2.72 years. At December 31, 2019 and 2018, the unamortized compensation expense was $1.4 million and $0.8 million respectively under our ESPP. The remaining unamortized expense will be recognized over the next 1.94 years. At December 31, 2019 and 2018, the unamortized compensation expense related to unvested restricted stock units was $2.5 million and $0.7 million, respectively. The remaining unamortized compensation expense will be recognized over the next 2.43 years.

Leases

Leases	12 Months Ended
	Dec. 31, 2019
Leases
Leases	8. Leases The Company leases office and laboratory space in Monrovia, CA under a lease that continues through June 2020, with an option to renew for an additional five years. The Company also leases office space in San Diego, CA through July 2020 which includes an option to renew for an additional five years. The Company assesses that it is unlikely to exercise the option to extend this lease. The Company leases additional office space in San Diego, CA through August 2022, with an option to extend for an additional five years. The Company assesses that it is unlikely to exercise the option to extend the lease term. The Company’s lease agreements do not contain any residual value guarantees or restrictive covenants. As of December 31, 2019, the Company did not have additional operating leases that have not yet commenced. The following table reconciles the undiscounted cash flows for the operating leases at December 31, 2019 to the operating lease liabilities recorded on the balance sheet (in thousands): ​ ​ ​ ​ Years ending December 31, ​ ​ 2020 ​ $ 2,703 2021 ​ ​ 2,588 2022 ​ ​ 2,208 2023 ​ ​ 1,352 2024 ​ ​ 1,371 Thereafter ​ ​ 2,282 Total undiscounted lease payments ​ ​ 12,504 Less: Imputed interest ​ ​ (1,770) Present value of lease payments ​ $ 10,734 ​ ​ ​ ​ Lease liabilities - short-term ​ $ 2,169 Lease liabilities - long-term ​ ​ 8,565 Total lease liabilities ​ $ 10,734 ​ Our operating lease cost and the cash payments for operating leases for the year ended December 31, 2019 were $2.7 million and $2.6 million, respectively. Rent expense for the year ended December 31, 2018 was $2.5 million. At December 31, 2019, the weighted-average remaining lease term for operating leases was 5.5 years, and the weighted average discount rate for operating leases is 5.5%.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies
Commitments and Contingencies	9. Commitments and Contingencies 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. We are obligated to make future payments to third parties under in-license agreements, including sublicense fees, royalties, and payments that become due and payable on the achievement of certain development and commercialization milestones. As the amount and timing of sublicense fees and the achievement and timing of these milestones are not probable and estimable, such commitments have not been included on our balance sheet. We have also entered into agreements with third party vendors which will require us to make future payments upon the delivery of goods and services in future periods. Guarantees In the normal course of business, we indemnify certain employees and other parties, such as collaboration partners and other parties that perform certain work on behalf of, or for the Company or take licenses to our technologies. We have agreed to hold these parties harmless against losses arising from our breach of representations or covenants, intellectual property infringement or other claims made against these parties in performance of their work with us. These agreements typically limit the time within which the party may seek indemnification by us and the amount of the claim. It is not possible to prospectively determine the maximum potential amount of liability under these indemnification agreements since we have not had any prior indemnification claims on which to base the calculation. Further, each potential claim would be based on the unique facts and circumstances of the claim and the particular provisions of each agreement. We are not aware of any potential claims and we did not record a liability as of December 31, 2019 and 2018.

Collaboration and Licensing Agr

Collaboration and Licensing Agreements	12 Months Ended
	Dec. 31, 2019
Collaboration and Licensing Agreements
Collaboration and Licensing Agreements	10. Collaboration and Licensing Agreements Following is a summary description of the material revenue arrangements, including arrangements that generated revenue in the period ended December 31, 2019, 2018, and 2017. The revenue reported for each agreement has been adjusted to reflect the adoption of ASC 606 for each period presented. Genentech In February 2019, the Company entered into a collaboration and license agreement (the Genentech Agreement) with Genentech, Inc. and F. Hoffman-La Roche Ltd (collectively, Genentech) for the development and commercialization of novel IL-15 collaboration products (Collaboration Products), including XmAb24306, the Company’s IL-15/IL-15Ra candidate. Under the terms of the Genentech Agreement, Genentech received an exclusive worldwide license to XmAb24306 and other Collaboration Products, including any new IL-15 programs identified during the joint research collaboration. Genentech and Xencor will jointly collaborate on worldwide development of XmAb24306 and potentially other Collaboration Products with Genentech maintaining all worldwide commercialization rights, subject to Xencor having an option to co-promote in the United States. Xencor has the right to perform clinical studies of Collaboration Products in combination with other therapeutic agents at its own cost, subject to certain restrictions. The term of the Genentech Agreement will continue on a program-by-program and country-by-country basis until there are no remaining payment obligations from Genentech to Xencor with respect to Collaboration Products. Genentech may terminate the Genentech Agreement in its entirety or on a Collaboration Product-by-Collaboration Product basis by providing prior written notice. Xencor may terminate the Agreement on a Collaboration Product-by-Collaboration Product basis under certain circumstances. In the event of a termination of any individual Collaboration Product or the Genentech Agreement in its entirety, the relevant rights revert to Xencor subsequent to negotiation of a termination agreement with Genentech. The Company received a $120.0 million upfront payment and is eligible to receive up to an aggregate of $160.0 million in clinical milestone payments for XmAb24306 and up to $180.0 million in clinical milestone payments for each new Collaboration Product. The Company is also eligible to receive 45% share of net profits for sales of XmAb24306 and other Collaboration Products, while also sharing in net losses at the same percentage rate. The parties will jointly share in development and commercialization costs for all programs designated as a development program under the Genentech Agreement at the same percentage rate, while Genentech will bear launch costs entirely. The initial 45% profit-cost share percentage is subject to a one-time downward adjustment at the Company’s discretion and convertible to a royalty under certain circumstances. Pursuant to the Genentech Agreement, XmAb24306 is designated as a development program and all costs incurred for developing XmAb24306 from the effective date of the Genentech Agreement are being shared with Genentech under the initial cost-sharing percentage. Under the Genentech Agreement, the Company and Genentech will conduct joint research activities for a two-year period to identify and discover additional IL-15 candidates developed from the Company’s cytokine and bispecific technologies. The two-year research term may be extended an additional year if both parties agree. The Company and Genentech are each responsible for their own costs in conducting the research activities. The Company is eligible for clinical milestone payments for new Collaboration Products identified from the research efforts. The Company evaluated the Genentech Agreement under the provisions of ASU No. 2014-09, Revenue from Contracts with Customers Collaborative Arrangements The Company identified the following performance obligations under the Genentech Agreement: (i) the license of XmAb24306 and (ii) research services during a two-year period to identify up to potentially nine additional IL-15 candidates, each a separate research program and a separate performance obligation. The Company determined that the license and each of the potential research programs are separate performance obligations because they are capable of being distinct and are distinct in the context of the Genentech Agreement. The license to XmAb24306 has standalone functionality as Genentech has exclusive worldwide rights to the program, including the right to sublicense to third parties. Genentech has significant experience and capabilities in developing and commercializing drug candidates similar to XmAb24306, and Genentech is capable of performing these activities without the Company’s involvement. Upon the transfer of the license of XmAb24306, Genentech could develop and commercialize XmAb24306 without further assistance from the Company. The Company determined that the research services for each potential additional IL-15 candidate and research program were separate standalone performance obligations. The Genentech Agreement provides an outline of an integrated research plan for the programs to be conducted by the two companies, and the research activities are separate and distinct from the license to XmAb24306. The Company determined the standalone selling price of the license to be $114.4 million using the adjusted market assessment approach considering similar collaboration and license agreements and transactions. The standalone selling price for the research activities for all nine of the potential IL-15 programs to be performed during the research term was determined to be $8.5 million using the expected cost approach which was derived from the Company’s experience and information from providing similar research activities to other parties. The Company determined that the transaction price of the Genentech Agreement at inception was $120.0 million consisting of the upfront payment. The potential milestones are not included in the transaction price as these are contingent on future events and the Company would not recognize these in revenue until it is not probable that these would not result in significant reversal of revenue amounts in future periods. The Company will re-assess the transaction price at each reporting period and when event outcomes are resolved or changes in circumstances occur. The Company allocated the transaction price to each of the separate performance obligations using the relative standalone selling price with $111.7 million allocated to the license to XmAb24306 and $8.3 million allocated to the research services. The Company recognized the $111.7 million allocated to the license when it satisfied its performance obligation and transferred the license to Genentech in March 2019. The license was transferred upon the effective date of the Genentech Agreement and when the Company subsequently transferred certain data related to the program to Genentech. The $8.3 million allocated to the research activities is being recognized over a period of time through the end of the research term that services are rendered as we determine that the input method is the appropriate approach to recognize income for such services. A total of $2.2 million of revenue related to the research activities was recognized in the year ended December 31, 2019. For the year ended December 31, 2019, we recognized $113.9 million of income from the Genentech Agreement. As of December 31, 2019, there is a $0.9 million payable related to cost-sharing development activities during the fourth quarter of 2019 for the XmAb24306 program. There is $6.1 million in deferred revenue as of December 31, 2019 which reflects our obligation to perform research services during the research term. Astellas Effective March 29, 2019, the Company entered into a Research and License Agreement (Astellas Agreement) with Astellas Pharma Inc. (Astellas) pursuant to which the Company and Astellas will conduct a discovery program to characterize compounds and products for development and commercialization. Under the Astellas Agreement, Astellas was granted a worldwide exclusive license, with the right to sublicense products in the field created by the research activities. Pursuant to the Astellas Agreement, the Company will apply its bispecific Fc technology to research antibodies provided by Astellas to generate bispecific antibody candidates and will conduct limited testing and characterization of the bispecific candidates and return the candidates to Astellas for development and commercialization. The activities will be conducted under a research plan agreed to by both parties to the Astellas Agreement. Astellas will assume full responsibility for development and commercialization of the antibody candidate. Pursuant to the Astellas Agreement, the Company received an upfront payment of $15.0 million and is eligible to receive up to $240.0 million in milestones which include $32.5 million in development milestones, $57.5 million in regulatory milestones and $150.0 million in sales milestones. If commercialized, the Company is eligible to receive royalties on net sales that range from the high-single to low-double digit percentages. We evaluated the Astellas Agreement under ASC 606 and identified the performance obligations under the Agreement to be (i) delivery of bispecific antibodies to Astellas from the antigen provided by Astellas and (ii) research activities against the bispecific antibodies as outlined in the research plan. The Company determined that the license to the bispecific antibodies is not a separate performance obligation because it is not capable of being distinct, the license to the antibodies cannot be separated from the underlying antibodies. Astellas will control and benefit from the antibodies that are delivered. The Astellas Agreement provides Astellas the right to sublicense the antibody to third parties and Astellas has significant experience and capabilities in developing and commercializing clinical candidates and is capable of performing these activities from the delivered antibodies without the Company’s involvement. The Company determined the standalone selling price of the bispecific deliverable to be $17.1 million using the income approach by calculating a risk adjusted net present value of the potential revenue that could be earned from the arrangement. The standalone selling price for the research activities to be performed was determined to be $1.4 million using the expected cost approach which was derived from the Company’s experience and information from providing similar research activities to other customers. The Company determined that the transaction price of the Astellas Agreement at inception was $15.0 million consisting of the upfront payment. The potential milestones are not included in the transaction price as these are contingent on future events and the Company would not recognize these in revenue until it is not probable that these would not result in significant reversal of revenue amounts in future periods. The Company will re-assess the transaction price at each reporting period and when event outcomes are resolved or changes in circumstances occur. The Company allocated the transaction price to each of the separate performance obligations using the relative standalone selling price with $13.6 million allocated to delivery of the bispecific antibodies and the remainder of $1.4 million was allocated to the research activities. The Company recognized the $13.6 million allocated to the bispecific antibodies when it satisfied its performance obligation and transferred the bispecific antibodies to Astellas. Astellas transferred the research antibodies to the Company and the Company applied its bispecific technologies to and transferred the completed antibodies to Astellas in June 2019. The $1.4 million allocated to the research activities is being recognized as the research services are being completed over the period of time the Company expects to complete the activities under the research plan. We recognized $14.0 million of revenue under this arrangement for the year ended December 31, 2019. There is $1.0 million in deferred revenue as of December 31, 2019 related to our obligation to complete research activities under the Astellas Agreement. Novartis In June 2016, the Company entered into a Collaboration and License Agreement (Novartis Agreement) with Novartis Institutes for BioMedical Research, Inc. (Novartis), to develop and commercialize bispecific and other Fc engineered antibody drug candidates using the Company’s proprietary XmAb® technologies and drug candidates. Pursuant to the Novartis Agreement: ● The Company granted Novartis certain exclusive rights to research, develop and commercialize XmAb14045 and XmAb13676 (plamotamab), two development stage products that incorporate the Company’s bispecific Fc technology; ● The Company will apply its bispecific technology in up to four target pair antibodies identified by Novartis (each a Global Discovery Program); and ● The Company will provide Novartis with a non-exclusive license to certain of its Fc technologies to apply against up to ten targets identified by Novartis. In December 2018, Novartis notified the Company it was terminating its rights with respect to the plamotamab program, which became effective June 2019. Under the Novartis Agreement, Novartis is responsible to fund its share of plamotamab development costs through June 2020. In November 2019, the Company and Novartis amended the Agreement and Novartis paid the Company $1.4 million in settlement of its projected remaining cost-sharing due for the plamotamab program. Pursuant to the Novartis Agreement, the Company will apply its bispecific technology to up to four target pair antibodies selected, if available for exclusive license to Novartis and not subject to a Company internal program. The Company will apply its bispecific technology to generate bispecific antibody candidates from starting target pair antibodies provided by Novartis for each of the four Global Discovery Programs and return the bispecific product candidate to Novartis for further testing, development and commercialization. Novartis has the right to substitute up to four of the original selected target pair antibodies during the research term provided that Novartis has not submitted and received allowance for an Investigational New Drug Application (IND) application with the Company provided bispecific antibody candidate. The research term is five years from the date of the Novartis Agreement. We completed delivery of a Global Discovery Program in 2017 and delivery of a second Global Discovery Program in 2018. In December 2019, Novartis dosed a patient in a Phase 1 study with an undisclosed bispecific antibody that is a Global Discovery Program, and we received a $10.0 million milestone payment. Novartis will assume full responsibility for development and commercialization of each product candidate under each of the Global Discovery Programs. The Company evaluated the Novartis Agreement under the new revenue recognition standard ASC 606 and concluded that Novartis is a customer. The Company identified the following performance obligations that it deemed to be distinct at the inception of the contract: ● License to certain rights to our XmAb14045 and plamotamab; ● Develop four bispecific antibody drug candidates against four targets identified by Novartis; and ● License to our Fc technologies for up to 10 targets identified and selected by Novartis. The Company considered the licenses as functional intellectual property as Novartis has the right to access its technology and such technology is functional to Novartis at the time that the Company provides access. Under the Novartis Agreement, Novartis has substitution rights under each discovery program provided it has not advanced to submitting an IND. The Company’s obligation to provide services related to the discovery programs, and Novartis’ right to substitute programs is limited to the five-year period from the date of the Novartis agreement. The Company determined the transaction price at inception is the $150.0 million upfront payment to be allocated to the performance obligations. The Novartis Agreement includes variable consideration for potential future milestones and royalties that were contingent on future success factors for development programs. The Company used the “most likely” method to determine the variable consideration. In the third quarter of 2019, the Company recorded a $10.0 million development milestone related to a Global Discovery program, and this amount was included in the transaction price as uncertainty associated with it has been resolved. None of the development, regulatory or sales milestones or royalties were included in the transaction price. The Company will re-evaluate the transaction price in each reporting period as uncertain events are resolved or other changes in circumstances occur. The Company determined the transaction price at inception of the Novartis Agreement and allocated it to the various performance obligations using the standalone selling price which is comparable to the relative selling price methodology used in the original accounting treatment for the transaction. The transaction price of $160.0 million was allocated to the performance obligations as follows: * $27.1 million to certain rights to the XmAb14045 program; * $31.4 million to certain rights to the plamotamab program; * $90.2 million to the four Global Discovery Programs; and * $11.3 million to the Fc licenses. Under ASC 606, revenue is recognized at the time that the Company’s performance obligation for each Global Discovery is completed upon delivery of each discovery program to Novartis. The Company delivered a discovery program to Novartis in 2017 and recognized $20.1 million of revenue in the period of delivery. In the third quarter of 2018, the Company delivered a second discovery program to Novartis and is recognizing an additional $20.0 million of revenue. In the third quarter of 2019, Novartis received notice of approval for an investigational new study (IND) from the Federal and Drug Administration (FDA) for an application submitted for a Global Discovery Program and we recognized $10.0 million of revenue. Under ASC 606 the entire amount of revenue allocated to the Fc licenses is being recognized at inception of the Novartis Agreement, the second quarter of 2016. During the year ended December 31, 2019, 2018 and 2017, the Company recognized $10.0 million, $20.0 million and $20.1 million of revenue respectively. As of December 31, 2019, there is a receivable of $12.2 million and $40.1 million in deferred revenue related to the arrangement. Amgen Inc. In September 2015, the Company entered into a research and license agreement (the Amgen Agreement) with Amgen Inc. (Amgen) to develop and commercialize bispecific antibody product candidates using the Company’s proprietary XmAb® bispecific Fc technology. Under the Amgen Agreement, the Company granted an exclusive license to Amgen to develop and commercialize bispecific drug candidates from the Company’s preclinical program that bind the CD38 antigen and the cytotoxic T-cell binding domain CD3, (the CD38 Program). The Company also agreed to apply its bispecific technology to five previously identified Amgen provided targets (each a Discovery Program). The Company received a $45.0 million upfront payment and milestones totaling $15.5 million from Amgen and is eligible to receive up to $600.0 million in future development, regulatory and sales milestones in total for programs in development and is eligible to receive royalties on any global net sales of products. Pursuant to the Amgen Agreement, the Company applied its bispecific technology to five Discovery Programs antibody molecules provided by Amgen that bind Discovery Program targets and returned the bispecific product candidates to Amgen for further testing, development and commercialization. The initial research term was three years from the date of the Amgen Agreement, but Amgen, pursuant to its option, requested an extension of one year. The Company received research funding for the additional services provided during the extended research term. Amgen will assume full responsibility for development and commercialization of product candidates under each of the Discovery Programs. The Company evaluated the Amgen Agreement under ASC 606 and determined that it is a customer and that delivery of the CD38 Program and each of the five Discovery Programs represent the performance obligations under the contract. The Company determined the transaction price at inception is the $45.0 million upfront payment to be allocated to the performance obligations. The Amgen Agreement includes variable consideration for potential future milestones and royalties that were contingent on future success factors for development programs. The Company used the “most likely” method to determine the variable consideration. In the fourth quarter of 2017, the Company received a $10.0 million development milestone related to the CD38 program, now AMG 424, and this payment was included in the transaction price as uncertainty associated with it has been resolved. In the fourth quarter of 2018, the Company received a $0.5 million preclinical milestone related to one of the Discovery Programs. In the third quarter of 2019, the Company recognized a $5.0 million milestone related to one of the Discovery Programs.No other development, regulatory or sales milestones or royalties were included in the transaction price. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. In allocating the transaction price determined at inception, the Company determined that ASC 606 provides the use of a standalone selling price for the transaction. The transaction price of $60.5 million was allocated to the performance obligations as follows: * $23.75 million to the CD38 program and * $36.75 million in total to the five Discovery Programs Under ASC 606, the amount of revenue recognized for the CD38 program is recognized at the inception of the contract when delivery of the CD38 program and materials was transferred to Amgen. The $10.0 million milestone revenue was recognized in the period that the uncertainty regarding the event is resolved, i.e. when the milestone event occurred. The Company completed performance obligations for the five Discovery Programs in 2016 when all five of the Discovery Programs were delivered to Amgen. In the fourth quarter of 2018, a $0.5 million milestone payment was received in connection with a preclinical development of a Discovery Program. In the third quarter of 2019, a $5.0 million milestone was recognized in connection with a development milestone for a Discovery Program. In the third quarter of 2018, the Company and Amgen agreed upon additional scope of work to be performed by the Company; the work was completed in 2018, and the Company recorded additional revenue of $0.1 million for the additional services provided. During the years ended December 31, 2019, 2018 and 2017, the Company recognized $5.0 million, $0.6 million and $10.0 million in revenue, respectively, under this arrangement. As of December 31, 2019, there was a $5.0 million receivable, and there was no deferred revenue related to the arrangement. MorphoSys AG In June 2010, the Company entered into a Collaboration and License Agreement with MorphoSys AG (MorphoSys), which was subsequently amended in March 2012. The agreement provided us an upfront payment of $13.0 million in exchange for an exclusive worldwide license to the Company’s patents and know-how to research, develop and commercialize our XmAb5574 product candidate (subsequently renamed MOR208 and tafasitamab) with the right to sublicense under certain conditions. If certain developmental, regulatory and sales milestones are achieved, the Company is eligible to receive future milestone payments and royalties. In June 2017, MorphoSys initiated a Phase 3 clinical trial under the arrangement for which the Company received a milestone payment of $12.5 million. The Company recognized the payment as revenue in the period that the milestone event occurred. The Company recognized $12.5 million of revenue for the year end December 31, 2017. There were no revenues recognized under this arrangement for the years ended December 31, 2019 and 2018. As of December 31, 2019, the Company has no deferred revenue related to this agreement. Alexion Pharmaceuticals, Inc. In January 2013, the Company entered into an option and license agreement with Alexion Pharmaceuticals, Inc. (Alexion). Under the terms of the agreement, the Company granted to Alexion an exclusive research license, with limited sublicensing rights, to make and use our Xtend technology to evaluate and advance compounds against six different target programs. Alexion exercised its rights to one target program, ALXN1210, which is now marketed as Ultomiris. The Company is eligible to receive contractual milestones for certain development, regulatory and commercial achievements. If licensed products are successfully commercialized, the Company is also entitled to receive royalties based on a percentage of net sales of such products sold by Alexion, its affiliates or its sub licensees, which percentage is in the low single digits. Alexion’s royalty obligations continue on a product-by-product and country-by-country basis until the expiration of the last-to-expire valid claim in a licensed patent covering the applicable product in such country. In the third quarter of 2018, Alexion completed certain regulatory submissions for Ultomiris, and the Company received $9.0 million in milestone payments. In the fourth quarter of 2018, Alexion completed certain regulatory submissions for Ultomiris and also received FDA marketing approval, and the Company received $11.0 million in milestone payments. In the second and third quarter of 2019, Alexion completed certain regulatory submissions for Ultomiris, and the Company received a total of $8.0 million in milestone payments. During 2019, the Company also recorded royalty revenue of $5.0 million in connection with reported net sales of Ultomiris by Alexion. The Company determined Alexion to be a customer and the license of the Company’s Xtend intellectual property is functional intellectual property, distinct and is the only performance obligation under the agreement. Under ASC 606 the upfront payment was recognized at inception of the agreement when Alexion was provided access to the technology. The total revenue recognized under this arrangement was $13.0 million and $20.0 million for the years ended December 31, 2019 and 2018, respectively. There was no revenue recognized for the year ended December 31, 2017. As of December 31, 2019, there is a receivable of $4.1 million, and there is no deferred revenue related to this agreement. CSL Limited In February 2009, the Company entered into a research license and commercialization agreement with CSL Limited (CSL). Under the agreement, the Company provided CSL with a research license to our Fc Cytotoxic technology and options to non-exclusive commercial licenses. CSL elected to exercise one commercial license for a compound, CSL362. In 2013 CSL sublicensed CSL362 (now called talacotuzumab) to Janssen Biotech Inc. (Janssen Biotech). In March 2017, CSL, through its sub-licensee, Janssen Biotech, initiated a Phase 3 clinical trial for CSL362 and the Company received a milestone payment of $3.5 million. There was no revenue recognized for the years ended December 31, 2019 and 2018. Total revenue recognized for the year ended December 31, 2017 was $3.5 million. As of December 31, 2019, there is no deferred revenue related to this agreement. INmune Bio, Inc. In October 2017, the Company entered into a License Agreement with INmune Bio, Inc. (INmune). Under the terms of the agreement, the Company provided INmune with an exclusive license to certain rights to a proprietary protein, XPRO1595. Under the agreement the Company received an upfront payment of $100,000, a 19% fully diluted equity interest in INmune and an option to acquire additional shares of INmune. The Company is eligible to receive a percentage of sublicensing revenue received for XPRO1595 and also royalties in the mid-single digit percent range on the sale of approved products. The equity interest in INmune constituted 1,585,000 shares of common stock, and the option is to purchase an additional 10% of the fully diluted interest in INmune for $10.0 million. In 2018, INmune filed a registration statement on a Form S-1 with the Securities and Exchange Commission (SEC) which was declared effective by the SEC on December 19, 2018. Under ASC 606, the Company determined that the performance obligation under the agreement was the license to XPRO1595 and performance occurred at the effective date of the agreement. The total consideration under the agreement was determined to be $100,000 as the equity interest and the option had an insignificant fair value. The Company recognized $100,000 as revenue related to the agreement for the year ended December 31, 2017 and did not recognize any revenue related to the agreement for the years ended December 31, 2019 or 2018. There is no deferred revenue as of December 31, 2019 related to this agreement. Vir Biotechnology, Inc. In the third quarter of 2019, the Company entered into a Patent License Agreement (the VirBio Agreement) with VIR Biotechnology (VirBio) pursuant to which the Company provided a non-exclusive license to its Xtend technology for up to two targets. Under the terms of the VirBio Agreement, the Company received an upfront payment and is eligible to receive total milestones of $155.25 million which include $5.25 million of development milestones, $30.0 million of regulatory milestones and $120.0 million of sales milestones. In addition, the Company is eligible to receive royalties on the net sales of approved products in the low-single digits. The Company evaluated the VirBio Agreement and determined that the single performance obligation was access to a non-exclusive license to certain patents of the Company which were transferred to VirBio upon execution of the VirBio Agreement in July 2019. The Company recognized $0.8 million of license and milestone revenue related to the agreement for the year ended December 31, 2019. There is no deferred revenue as of December 31, 2019 related to this agreement. Revenue Earned The $156.7 million, $40.6 million and $46.2 million of revenue recorded for the years ended December 31, 2019, 2018 and 2017, respectively, were earned principally from the following licensees (in millions): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2019 ​ 2018 ​ 2017 Amgen $ 5.0 $ 0.6 $ 10.0 ​ Alexion ​ ​ 13.0 ​ 20.0 ​ — ​ Astellas ​ ​ 14.0 ​ — ​ — ​ CSL ​ ​ — ​ — ​ 3.5 ​ Genentech ​ ​ 113.9 ​ — ​ — ​ MorphoSys ​ ​ — ​ — ​ 12.5 ​ Novartis ​ ​ 10.0 ​ ​ 20.0 ​ ​ 20.1 ​ Other ​ ​ 0.8 ​ — ​ 0.1 ​ Total ​ $ 156.7 ​ $ 40.6 ​ $ 46.2 ​ The below table summarizes the disaggregation of revenue recorded for the years ended December 31, 2019, 2018 and 2017 (in millions): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2019 ​ 2018 ​ 2017 Research collaboration $ 16.3 $ 20.1 $ 20.1 Milestone ​ ​ 23.2 ​ 20.5 ​ 26.0 Licensing ​ ​ 112.2 ​ — ​ 0.1 Royalties ​ ​ 5.0 ​ — ​ — Total ​ $ 156.7 ​ $ 40.6 ​ $ 46.2 A portion of our revenue is earned from collaboration partners outside the United States. Non-U.S. revenue is denominated in U.S. dollars. A breakdown of our revenue from U.S. and non-U.S. sources for the years ended December 31, 2019, 2018 and 2017 is as follows (in millions): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2019 ​ 2018 ​ 2017 U.S. Revenue $ 142.7 $ 40.6 $ 30.2 ​ Non-U.S. Revenue ​ ​ 14.0 ​ ​ — ​ ​ 16.0 ​ Total ​ $ 156.7 ​ $ 40.6 ​ $ 46.2 ​ Remaining Performance Obligations and Deferred Revenue Our remaining performance obligations are delivery of two additional Global Discovery Programs under the Novartis Agreement and conducting research activities pursuant to research plans under the Genentech and Astellas Agreements. As of December 31, 2019 and 2018, we have deferred revenue of $47.1 million and $40.1 million, respectively. As of December 31, 2019, $45.2 million of deferred revenue was classified as current liabilities as our obligations to perform servic

401(k) Plan

401(k) Plan	12 Months Ended
	Dec. 31, 2019
401(k) Plan
401(k) Plan	11. 401(k) Plan We have a 401(k)-plan covering all full-time employees. Employees may make pre-tax contributions up to the maximum allowable by the Internal Revenue Code. Effective January 1, 2018, the Company contributes 100% of the first 1% of participating employees’ contribution and 50% of the next 5% of participating employees’ contribution, for a maximum of 3.5% employer contribution. Participants are immediately vested in their employee contributions; employer contributions are vested over a three-year period with one

Condensed Quarterly Financial D

Condensed Quarterly Financial Data (unaudited)	12 Months Ended
	Dec. 31, 2019
Condensed Quarterly Financial Data (unaudited)
Condensed Quarterly Financial Data (unaudited)	12. Condensed Quarterly Financial Data (unaudited) The following table contains selected unaudited financial data for each quarter of 2019 and 2018. The unaudited information should be read in conjunction with the Company’s financial statements and related notes included elsewhere in this Annual Report. The Company believes that the following information reflects all normal recurring adjustments necessary for a fair presentation of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period. Quarterly Financial Data (in thousands, except per share data): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 Quarter Ended ​ March 31, June 30, September 30, December 31, Total revenue ​ $ 111,939 ​ $ 19,485 ​ $ 21,760 ​ $ 3,516 ​ Income (loss) from operations ​ 78,244 ​ (19,572) ​ (14,276) ​ (30,572) ​ Net income (loss) ​ 80,045 ​ (16,034) ​ (10,224) ​ (26,912) ​ Basic net income (loss) per common share ​ 1.42 ​ (0.28) ​ (0.18) ​ (0.47) ​ Diluted net income (loss) per common share ​ ​ 1.38 ​ ​ (0.28) ​ ​ (0.18) ​ ​ (0.47) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2018 Quarter Ended ​ ​ March 31, ​ June 30, ​ September 30, ​ December 31, Total revenue $ — ​ $ — ​ $ 29,039 ​ $ 11,564 ​ Income (loss) from operations ​ (30,649) ​ (28,290) ​ 651 ​ (21,082) ​ Net income (loss) ​ (29,493) ​ (25,869) ​ 3,150 ​ (18,197) ​ Basic net income (loss) per common share ​ (0.62) ​ (0.46) ​ 0.06 ​ (0.32) ​ Diluted net income (loss) per common share ​ ​ (0.62) ​ ​ (0.46) ​ ​ 0.05 ​ ​ (0.32) ​ ​

Subsequent Event

Subsequent Event	12 Months Ended
	Dec. 31, 2019
Subsequent Event
Subsequent Event	13. Subsequent Event Gilead and Aimmune Agreements In January and February 2020, the Company entered into license agreements with Gilead and with Aimmune, respectively for the license of Company technologies and drug candidates. Under the Gilead agreement, the Company licensed restricted access to its cytotoxic and Xtend technologies and the Company received a $6.0 million upfront payment and is eligible to receive additional milestones and potential royalties under the license agreement. Under the Aimmune agreement, the Company licensed the worldwide exclusive rights to its XmAb7195 drug candidate, and the Company will receive a $5.0 million upfront payment and common stock of Aimmune with an aggregate value of $5.0 million. Aimmune will be responsible for all development activities for XmAb7195 and the Company is eligible to receive additional milestones and potential royalties under the arrangement. ​

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Polices)	12 Months Ended
	Dec. 31, 2019
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation The Company’s financial statements as of December 31, 2019, 2018, and 2017 and for the years then ended have been prepared in accordance with accounting principles generally accepted in the United States (U.S.).
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Significant estimates include useful lives of long-lived assets, the periods over which certain revenues and expenses will be recognized including collaboration revenue recognized from non-refundable upfront licensing payments, the amount of non-cash compensation costs related to share-based payments to employees and non-employees and the period over which these costs are expensed.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Pronouncements adopted in 2019 Pronouncements not yet effective In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments Codification Improvements to Topic 326, Financial Instruments – Credit Losses In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement In August 2018, the FASB issued ASU No. 2018-15, Intangibles – Goodwill and Other – Internal Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract In October 2018, the FASB issued ASU No. 2018-17, Consolidation (Topic 810): Targeted Improvements to Related Party Guidance for Variable Interest Entities In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction Between Topic 808 and Topic 606 In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes
Revenue Recognition	Revenue Recognition We have, to date, earned revenue from research and development collaborations, which may include research and development services, licenses of our internally developed technologies, licenses of our internally developed drug candidates, or combinations of these. The terms of our license and research and development and collaboration agreements generally include non-refundable upfront payments, research funding, co-development reimbursements, license fees and, milestone and other contingent payments to us for the achievement of defined collaboration objectives and certain clinical, regulatory and sales-based events, as well as royalties on sales of any commercialized products. The terms of our licensing agreements include non-refundable upfront fees, annual licensing fees, and contractual payment obligations for the achievement of pre-defined preclinical, clinical, regulatory and sales-based events by our partners. The licensing agreements also include royalties on sales of any commercialized products by our partners. We recognize revenue through the five-step process in accordance with ASC 606 Revenue Recognition when control of the promised goods or services is transferred to our customers in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services.
Deferred Revenue	Deferred Revenue Deferred revenue arises from payments received in advance of the culmination of the earnings process. We have classified deferred revenue for which we stand ready to perform within the next 12 months as a current liability. We recognize deferred revenue as revenue in future periods when the applicable revenue recognition criteria have been met. The total amounts reported as deferred revenue were $47.1 million and $40.1 million at December 31, 2019 and 2018, respectively.
Research and Development Expenses	Research and Development Expenses Research and development expenses include costs we incur for our own and for our collaborators’ research and development activities. Research and development costs are expensed as incurred. These costs consist primarily of salaries and benefits, including associated stock-based compensation, laboratory supplies, facility costs, and applicable overhead expenses of personnel directly involved in the research and development of new technology and products, as well as fees paid to other entities that conduct certain research development activities on our behalf. We estimate preclinical study and clinical trial expenses based on the services performed pursuant to the contracts with research institutions and clinical research organizations that conduct and manage preclinical studies and clinical trials on our behalf based on the actual time and expenses incurred by them. Further, we accrue expenses related to clinical trials based on the level of patient enrollment and activity according to the related agreement. We monitor patient enrollment levels and related activity to the extent reasonably possible and adjust estimates accordingly. We capitalize acquired research and development technology licenses and third-party contract rights and amortize the costs over the shorter of the license term or the expected useful life. We review the license arrangements and the amortization period on a regular basis and adjust the carrying value or the amortization period of the licensed rights if there is evidence of a change in the carrying value or useful life of the asset.
Cash and Cash Equivalents	We consider cash equivalents to be only those investments which are highly liquid, readily convertible to cash and which mature within three months from the date of purchase.
Marketable Securities	Marketable Securities The Company has an investment policy that includes guidelines on acceptable investment securities, minimum credit quality, maturity parameters and concentration and diversification. The Company invests its excess cash primarily in marketable debt securities issued by investment grade institutions. The Company considers its marketable debt securities to be “available-for-sale”, as defined by authoritative guidance issued by the FASB. These assets are carried at fair value and the unrealized gains and losses are included in accumulated other comprehensive income (loss). Accrued interest on marketable debt securities is included in marketable securities. Accrued interest was $2.7 million and $2.3 million at December 31, 2019 and 2018, respectively. If a decline in the value of a marketable security in the Company’s investment portfolio is deemed to be other-than-temporary, the Company writes down the security to its current fair value and recognizes a loss as a charge against income. The Company reviews its portfolio of marketable debt securities, using both quantitative and qualitative factors, to determine if declines in fair value below cost are other-than-temporary.
Concentrations of Risk	Concentrations of Risk Cash, cash equivalents and marketable debt securities are financial instruments that potentially subject the Company to concentrations of risk. We invest our cash in corporate debt securities and U.S. sponsored agencies with strong credit ratings. We have established guidelines relative to diversification and maturities that are designed to help ensure safety and liquidity. These guidelines are periodically reviewed to take advantage of trends in yields and interest rates. Cash and cash equivalents are maintained at financial institutions and, at times, balances may exceed federally insured limits. We have never experienced any losses related to these balances. Amounts on deposit in excess of federally insured limits at December 31, 2019 and 2018 approximated $50.0 million and $26.0 million, respectively. We have payables with two service providers that represent 48% of our total payables and four service providers that represented 49% of our total payables at December 31, 2019 and 2018, respectively. We rely on three critical suppliers for the manufacture of our drug product for use in our clinical trials. While we believe that there are alternative vendors available, a change in manufacturing vendors could cause a delay in the availability of drug product and result in a delay of conducting and completing our clinical trials. No other vendor accounted for more than 10% of total payables at December 31, 2019 or 2018.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Our financial instruments primarily consist of cash and cash equivalents, marketable debt securities, accounts receivable, accounts payable and accrued expenses. Marketable debt securities and cash equivalents are carried at fair value. The fair value of the other financial instruments closely approximate their fair value due to their short maturities. The Company accounts for recurring and non-recurring fair value measurements in accordance with FASB Accounting Standards Codification (ASC) 820, Fair Value Measurements and Disclosures Level 1— Level 2— Level 3— The Company measures the fair value of financial assets using the highest level of inputs that are reasonably available as of the measurement date. The assets recorded at fair value are classified within the hierarchy as follows for the periods reported (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ Total ​ ​ ​ ​ ​ ​ Fair Value ​ Level 1 ​ Level 2 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money Market Funds in Cash and Cash Equivalents ​ $ 32,009 ​ $ 32,009 ​ $ — Corporate Securities ​ ​ 281,751 ​ ​ — ​ ​ 281,751 Government Securities ​ ​ 269,245 ​ ​ — ​ ​ 269,245 ​ ​ $ 583,005 ​ $ 32,009 ​ $ 550,996 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2018 ​ Total ​ ​ ​ ​ ​ ​ Fair Value ​ Level 1 ​ Level 2 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money Market Funds in Cash and Cash Equivalents ​ $ 18,270 ​ $ 18,270 ​ $ — Corporate Securities ​ ​ 104,967 ​ ​ — ​ ​ 104,967 Government Securities ​ ​ 399,256 ​ ​ — ​ ​ 399,256 ​ ​ $ 522,493 ​ $ 18,270 ​ $ 504,223 ​ Property and Equipment Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the assets. Expenditures for repairs and maintenance are charged to expense as incurred while renewals and improvements are capitalized. Useful lives by asset category are as follows: ​ ​ ​ ​ ​ ​ ​ Computers, software and equipment 3 - 5 years ​ Furniture and fixtures 5 - 7 years ​ Leasehold improvements 5 - 7 years or remaining ​ ​ ​ lease term, whichever is less ​ ​ Patents, Licenses, and Other Intangible Assets The cost of acquiring licenses is capitalized and amortized on the straight-line basis over the shorter of the term of the license or its estimated economic life, ranging from five 13 The carrying amount and accumulated amortization of patents, licenses, and other intangibles is as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2019 ​ 2018 Patents, definite life $ 10,597 $ 9,320 ​ Patents, pending issuance ​ ​ 7,266 ​ 5,644 ​ Licenses and other amortizable intangible assets ​ ​ 2,510 ​ 2,011 ​ Nonamortizable intangible assets (trademarks) ​ ​ 399 ​ 399 ​ Total gross carrying amount ​ ​ 20,772 ​ 17,374 ​ Accumulated amortization—patents ​ ​ (4,912) ​ (4,142) ​ Accumulated amortization—licenses and other ​ ​ (1,439) ​ (1,263) ​ Total intangible assets, net ​ $ 14,421 ​ $ 11,969 ​ ​ Amortization expense for patents, licenses, and other intangible assets was $0.9 million, $0.9 million and $0.8 million for the years ended December 31, 2019, 2018 and 2017, respectively. Future amortization expense for patent, licenses, and other intangible assets recorded as of December 31, 2019, and for which amortization has commenced, is as follows: ​ ​ ​ ​ ​ ​ ​ Year ended ​ ​ December 31, ​ ​ (in thousands) 2020 ​ $ 1,009 ​ 2021 ​ ​ 912 ​ 2022 ​ ​ 880 ​ 2023 ​ ​ 809 ​ 2024 ​ ​ 647 ​ Thereafter ​ ​ 2,365 ​ Total ​ $ 6,622 ​ ​ The above amortization expense forecast is an estimate. Actual amounts of amortization expense may differ from estimated amounts due to additional intangible asset acquisitions, impairment of intangible assets, accelerated amortization of intangible assets, and other events. As of December 31, 2019, the Company has $7.3 million of intangible assets which are in-process and have not been placed in service, and accordingly amortization on these assets has not commenced.
Property and Equipment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ Total ​ ​ ​ ​ ​ ​ Fair Value ​ Level 1 ​ Level 2 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money Market Funds in Cash and Cash Equivalents ​ $ 32,009 ​ $ 32,009 ​ $ — Corporate Securities ​ ​ 281,751 ​ ​ — ​ ​ 281,751 Government Securities ​ ​ 269,245 ​ ​ — ​ ​ 269,245 ​ ​ $ 583,005 ​ $ 32,009 ​ $ 550,996 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2018 ​ Total ​ ​ ​ ​ ​ ​ Fair Value ​ Level 1 ​ Level 2 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money Market Funds in Cash and Cash Equivalents ​ $ 18,270 ​ $ 18,270 ​ $ — Corporate Securities ​ ​ 104,967 ​ ​ — ​ ​ 104,967 Government Securities ​ ​ 399,256 ​ ​ — ​ ​ 399,256 ​ ​ $ 522,493 ​ $ 18,270 ​ $ 504,223
Patents, Licenses, and Other Intangible Assets	​ ​ ​ ​ ​ ​ ​ Computers, software and equipment 3 - 5 years ​ Furniture and fixtures 5 - 7 years ​ Leasehold improvements 5 - 7 years or remaining ​ ​ ​ lease term, whichever is less ​
Long-Lived Assets	Long-Lived Assets Management reviews long-lived assets which include fixed assets and amortizable intangibles for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset (or asset group) may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds the fair value of the assets. We did not recognize a loss from impairment for the years ended December 31, 2019, 2018 or 2017.
Income Taxes	Income Taxes We account for income taxes in accordance with accounting guidance which requires an asset and liability approach to financial accounting and reporting for income taxes. Deferred income tax assets and liabilities are computed annually for differences between the financial statement and tax bases of assets and liabilities that will result in taxable or deductible amounts in the future based on enacted tax laws and rates applicable to the periods in which the differences are expected to affect taxable income. Valuation allowances are established when necessary to reduce deferred tax assets to the amount expected to be realized. Income tax expense is the tax payable or refundable for the period plus or minus the change during the period in deferred tax assets and liabilities. We assess our income tax positions and record tax benefits for all years subject to examination based upon our evaluation of the facts, circumstances and information available at the reporting date. For those tax positions where there is greater than 50% likelihood that a tax benefit will be sustained, we have recorded the largest amount of tax benefit that may potentially be realized upon ultimate settlement with a taxing authority that has full knowledge of all relevant information. For those income tax positions where there is a 50% or less likelihood that a tax benefit will be sustained, no tax benefit has been recognized in the financial statements. We did not have any material uncertain tax positions at December 31, 2019 or 2018. Our policy is to recognize interest and penalties on taxes, if any, as a component of income tax expense. The Tax Cuts and Jobs Act of 2017 (TCJA) was enacted on December 22, 2017 and has several key provisions impacting the accounting for and reporting of income taxes. The most significant provisions reduced the U.S. corporate statutory tax rate from 35% to 21%, eliminated the corporate Alternative Minimum Tax (AMT) system, and made changes to the utilization and carryforward of net operating losses beginning on January 1, 2018. The tax reform provided for a refund of unused AMT carryforwards for years beginning after December 31, 2017. We recorded an income tax receivable as of December 31, 2019 and 2018 of $0.8 million and $1.6 million, respectively related to federal AMT carryforwards.
Stock-Based Compensation	Stock-Based Compensation We recognize compensation expense using a fair-value-based method for costs related to all share-based payments, including stock options and shares issued under our Employee Stock Purchase Plan (ESPP). Stock-based compensation cost related to employees and directors is measured at the grant date, based on the fair-value-based measurement of the award using the Black-Scholes method, and is recognized as expense over the requisite service period on a straight-line basis. We account for forfeitures when they occur. We recorded stock-based compensation and expense for stock-based awards to employees, directors and consultants of approximately $31.9 million, $20.5 million and $13.7 million for the years ended December 31, 2019, 2018 and 2017 respectively. Included in the 2019, 2018, and 2017 balances for total compensation expense is $0.7 million, $0.7 million and $0.5 million, respectively, relating to our ESPP. Options granted to individual service providers that are not employees or directors are accounted for at estimated fair value using the Black-Scholes option-pricing method and are subject to periodic re-measurement over the period during which the services are rendered.
Net Income (Loss) Per Share	Net Income (Loss) Per Share Basic net income (loss) per common share is computed by dividing the net income or loss by the weighted-average number of common shares outstanding during the period. Potentially dilutive securities were included in the diluted net income per common share calculation for 2019. We included 1,923,310 options to purchase shares of common stock and 13,131 shares of restricted stock units (RSUs) in the calculation of the weighted-average common shares outstanding used in computing diluted net income per common share. We excluded 1,022,623 shares of options and RSUs from the calculation for 2019 because the inclusion of such shares would have had an antidilutive effect. ​ In 2018 and 2017, we excluded all options and awards from the calculations because we reported net losses in the periods and the inclusion of such shares would have had an antidilutive effect. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ 2019 ​ 2018 ​ 2017 ​ ​ (in thousands, except share and per share data) Basic ​ ​ ​ ​ Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) attributable to common stockholders for basic net income (loss) per share ​ $ 26,875 ​ $ (70,409) ​ $ (38,486) ​ Denominator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average common shares outstanding ​ ​ 56,531,439 ​ 53,942,116 ​ 46,817,756 ​ Basic net income (loss) per common share ​ $ 0.48 ​ $ (1.31) ​ $ (0.82) ​ Diluted ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) attributable to common stockholders for diluted net income (loss) per share ​ $ 26,875 ​ $ (70,409) ​ $ (38,486) ​ Denominator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average number of common shares outstanding used in computing basic net income (loss) per common share ​ ​ 56,531,439 ​ 53,942,116 ​ 46,817,756 ​ Dilutive effect of employee stock options and ESPP ​ ​ 1,936,441 ​ — ​ — ​ Weighted-average number of common shares outstanding used in computing diluted net income (loss) per common share ​ ​ 58,467,880 ​ 53,942,116 ​ 46,817,756 ​ Diluted net income (loss) per common share ​ $ 0.46 ​ $ (1.31) ​ $ (0.82) ​ ​
Segment Reporting	Segment Reporting The Company determines its segment reporting based upon the way the business is organized for making operating decisions and assessing performance. The Company has only one operating segment related to the development of pharmaceutical products .

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Summary of Significant Accounting Policies
Schedule of assets recorded at fair value	The Company measures the fair value of financial assets using the highest level of inputs that are reasonably available as of the measurement date. The assets recorded at fair value are classified within the hierarchy as follows for the periods reported (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ Total ​ ​ ​ ​ ​ ​ Fair Value ​ Level 1 ​ Level 2 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money Market Funds in Cash and Cash Equivalents ​ $ 32,009 ​ $ 32,009 ​ $ — Corporate Securities ​ ​ 281,751 ​ ​ — ​ ​ 281,751 Government Securities ​ ​ 269,245 ​ ​ — ​ ​ 269,245 ​ ​ $ 583,005 ​ $ 32,009 ​ $ 550,996 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2018 ​ Total ​ ​ ​ ​ ​ ​ Fair Value ​ Level 1 ​ Level 2 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money Market Funds in Cash and Cash Equivalents ​ $ 18,270 ​ $ 18,270 ​ $ — Corporate Securities ​ ​ 104,967 ​ ​ — ​ ​ 104,967 Government Securities ​ ​ 399,256 ​ ​ — ​ ​ 399,256 ​ ​ $ 522,493 ​ $ 18,270 ​ $ 504,223 ​
Schedule of useful lives by asset category	​ ​ ​ ​ ​ ​ ​ Computers, software and equipment 3 - 5 years ​ Furniture and fixtures 5 - 7 years ​ Leasehold improvements 5 - 7 years or remaining ​ ​ ​ lease term, whichever is less ​
Schedule of finite-lived intangible assets	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2019 ​ 2018 Patents, definite life $ 10,597 $ 9,320 ​ Patents, pending issuance ​ ​ 7,266 ​ 5,644 ​ Licenses and other amortizable intangible assets ​ ​ 2,510 ​ 2,011 ​ Nonamortizable intangible assets (trademarks) ​ ​ 399 ​ 399 ​ Total gross carrying amount ​ ​ 20,772 ​ 17,374 ​ Accumulated amortization—patents ​ ​ (4,912) ​ (4,142) ​ Accumulated amortization—licenses and other ​ ​ (1,439) ​ (1,263) ​ Total intangible assets, net ​ $ 14,421 ​ $ 11,969 ​
Schedule of indefinite-lived intangible assets	The carrying amount and accumulated amortization of patents, licenses, and other intangibles is as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2019 ​ 2018 Patents, definite life $ 10,597 $ 9,320 ​ Patents, pending issuance ​ ​ 7,266 ​ 5,644 ​ Licenses and other amortizable intangible assets ​ ​ 2,510 ​ 2,011 ​ Nonamortizable intangible assets (trademarks) ​ ​ 399 ​ 399 ​ Total gross carrying amount ​ ​ 20,772 ​ 17,374 ​ Accumulated amortization—patents ​ ​ (4,912) ​ (4,142) ​ Accumulated amortization—licenses and other ​ ​ (1,439) ​ (1,263) ​ Total intangible assets, net ​ $ 14,421 ​ $ 11,969 ​
Future amortization expense for patents, licenses, and other intangible assets	​ ​ ​ ​ ​ ​ ​ Year ended ​ ​ December 31, ​ ​ (in thousands) 2020 ​ $ 1,009 ​ 2021 ​ ​ 912 ​ 2022 ​ ​ 880 ​ 2023 ​ ​ 809 ​ 2024 ​ ​ 647 ​ Thereafter ​ ​ 2,365 ​ Total ​ $ 6,622 ​
Schedule of basic and diluted net income (loss) per common share	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended December 31, ​ ​ 2019 ​ 2018 ​ 2017 ​ ​ (in thousands, except share and per share data) Basic ​ ​ ​ ​ Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) attributable to common stockholders for basic net income (loss) per share ​ $ 26,875 ​ $ (70,409) ​ $ (38,486) ​ Denominator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average common shares outstanding ​ ​ 56,531,439 ​ 53,942,116 ​ 46,817,756 ​ Basic net income (loss) per common share ​ $ 0.48 ​ $ (1.31) ​ $ (0.82) ​ Diluted ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Numerator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) attributable to common stockholders for diluted net income (loss) per share ​ $ 26,875 ​ $ (70,409) ​ $ (38,486) ​ Denominator: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average number of common shares outstanding used in computing basic net income (loss) per common share ​ ​ 56,531,439 ​ 53,942,116 ​ 46,817,756 ​ Dilutive effect of employee stock options and ESPP ​ ​ 1,936,441 ​ — ​ — ​ Weighted-average number of common shares outstanding used in computing diluted net income (loss) per common share ​ ​ 58,467,880 ​ 53,942,116 ​ 46,817,756 ​ Diluted net income (loss) per common share ​ $ 0.46 ​ $ (1.31) ​ $ (0.82) ​

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2019
Marketable Securities
Schedule of marketable securities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ Amortized Unrealized ​ Unrealized ​ ​ ​ Cost ​ Gains ​ Losses ​ Fair Value (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money Market Funds ​ $ 32,009 ​ $ — ​ $ — ​ $ 32,009 Corporate Securities ​ ​ 281,586 ​ ​ 195 ​ ​ (30) ​ ​ 281,751 Government Securities ​ ​ 268,239 ​ ​ 1,006 ​ ​ — ​ ​ 269,245 ​ ​ $ 581,834 ​ $ 1,201 ​ $ (30) ​ $ 583,005 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Reported as ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 32,009 Marketable securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 550,996 Total investments ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 583,005 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2018 ​ ​ ​ ​ ​ Gross ​ Gross ​ ​ ​ ​ Amortized Unrealized ​ Unrealized ​ ​ ​ Cost ​ Gains ​ Losses ​ Fair Value (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money Market Funds ​ $ 18,270 ​ $ — ​ $ — ​ $ 18,270 Corporate Securities ​ ​ 105,311 ​ ​ 1 ​ ​ (345) ​ ​ 104,967 Government Securities ​ ​ 399,873 ​ ​ 187 ​ ​ (804) ​ ​ 399,256 ​ ​ $ 523,454 ​ $ 188 ​ $ (1,149) ​ $ 522,493 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Reported as ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash and cash equivalents ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 18,270 Marketable securities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 504,223 Total investments ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ $ 522,493
Schedule of maturities of marketable securities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amortized Estimated ​ ​ Cost ​ Fair Value (in thousands) ​ ​ ​ ​ ​ ​ Mature in one year or less ​ $ 478,338 ​ $ 479,470 Mature after one year through five years ​ ​ 71,487 ​ ​ 71,526 ​ ​ $ 549,825 ​ $ 550,996
Schedule of unrealized losses on available-for-sale investments	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ ​ Less than 12 months ​ 12 months or greater ​ ​ ​ Fair value ​ ​ Unrealized losses ​ ​ Fair value ​ ​ Unrealized gain (losses) (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate Securities ​ $ 46,303 ​ $ (24) ​ $ 13,992 ​ $ (6) Government Securities ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ $ 46,303 ​ $ (24) ​ $ 13,992 ​ $ (6) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2018 ​ ​ Less than 12 months ​ 12 months or greater ​ ​ ​ Fair value ​ ​ Unrealized losses ​ ​ Fair value ​ ​ Unrealized losses (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Corporate Securities ​ $ 84,666 ​ $ (310) ​ $ 17,805 ​ $ (35) Government Securities ​ ​ 176,225 ​ ​ (672) ​ ​ 116,830 ​ ​ (132) ​ ​ $ 260,891 ​ $ (982) ​ $ 134,635 ​ $ (167)

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2019
Property and Equipment
Schedule of property and equipment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2019 ​ 2018 ​ ​ (in thousands) Computers, software and equipment $ 21,087 $ 16,292 ​ Furniture and fixtures ​ ​ 492 ​ 173 ​ Leasehold and tenant improvements ​ ​ 6,831 ​ 4,774 ​ ​ ​ ​ 28,410 ​ 21,239 ​ Less accumulated depreciation and amortization ​ (12,605) ​ (9,426) ​ ​ ​ $ 15,805 ​ $ 11,813 ​

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Taxes
Reconciliation of the federal statutory income tax rate to our effective income tax rate	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2019 ​ 2018 ​ 2017 Federal statutory income tax $ 5,709 $ (14,795) $ (13,243) ​ State and local income taxes ​ ​ 2,549 ​ (4,767) ​ (1,806) ​ Research and development credit ​ (6,747) ​ (6,170) ​ (5,554) ​ Stock based compensation ​ ​ 1,927 ​ ​ 444 ​ ​ 2,709 ​ Effect of the 2017 Tax Cut and Jobs Act ​ ​ — ​ ​ — ​ ​ 19,596 ​ State credit ​ ​ 1,725 ​ ​ — ​ ​ — ​ Other ​ ​ (301) ​ 414 ​ 720 ​ Net change in valuation allowance ​ ​ (4,550) ​ 24,874 ​ (2,885) ​ Income tax provision (benefit) ​ $ 312 ​ $ — ​ $ (463) ​
Schedule of tax effect of temporary differences that give rise to a significant portion of the deferred tax assets and liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2019 2018 ​ Deferred income tax assets ​ ​ ​ ​ ​ ​ ​ Net operating loss carryforwards ​ $ 36,891 ​ $ 49,889 ​ Research credits ​ ​ 28,415 ​ 23,151 ​ Depreciation ​ ​ 334 ​ 207 ​ Unrealized loss on securities ​ ​ — ​ 269 ​ Accrued compensation ​ ​ 4,788 ​ 1,097 ​ Deferred revenue ​ ​ 11,215 ​ 11,222 ​ State taxes ​ ​ 64 ​ — ​ Gross deferred income tax assets ​ ​ 81,707 ​ 85,835 ​ Valuation allowance ​ (77,389) ​ (82,537) ​ Net deferred income tax assets ​ ​ 4,318 ​ 3,298 ​ Deferred income tax liabilities ​ ​ ​ ​ ​ ​ ​ Patent costs ​ (3,736) ​ (3,142) ​ Licensing costs ​ (229) ​ (125) ​ Capitalized legal costs ​ (26) ​ (31) ​ Unrealized gain on securities ​ ​ (327) ​ ​ — ​ Gross deferred income tax liabilities ​ (4,318) ​ (3,298) ​ Net deferred income tax asset ​ $ — ​ $ — ​

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2019
Stock-Based Compensation
Schedule of total employee, director and non-employee stock-based compensation expense recognized	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, (in thousands) ​ 2019 ​ 2018 ​ 2017 General and administrative $ 8,854 $ 7,699 $ 5,617 ​ Research and development ​ ​ 22,997 ​ 12,849 ​ 8,034 ​ ​ ​ $ 31,851 ​ $ 20,548 ​ $ 13,651 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ ​ December 31, ​ (in thousands) ​ 2019 ​ 2018 ​ 2017 ​ Stock options $ 30,502 $ 19,537 $ 13,153 ​ ESPP ​ ​ 687 ​ 744 ​ 498 ​ RSUs ​ ​ 662 ​ 267 ​ — ​ ​ ​ $ 31,851 ​ $ 20,548 ​ $ 13,651 ​
Schedule of stock options outstanding	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ ​ 2019 ​ 2018 ​ 2017 Exercisable options ​ 3,950,965 ​ 3,058,659 ​ 2,558,941 ​ Weighted average exercise price per share of exercisable options ​ $ 17.79 ​ $ 15.12 ​ $ 11.06 ​ Weighted average grant date fair value per share of options granted during the year ​ $ 20.74 ​ $ 18.06 ​ $ 16.92 ​ Options available for future grants ​ 3,975,160 ​ 3,576,574 ​ 3,394,691 ​ Weighted average remaining contractual life ​ 7.32 ​ 7.51 ​ 7.62 ​
Summary of stock option activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted- ​ ​ ​ ​ ​ ​ Weighted- ​ Average ​ ​ ​ ​ ​ ​ ​ Average ​ Remaining ​ ​ ​ ​ ​ ​ ​ Exercise ​ Contractual ​ Aggregate ​ ​ Number of ​ Price ​ Term ​ Intrinsic Value ​ ​ Shares ​ (Per Share) (1) ​ (in years) ​ (in thousands) (2) Balances at December 31, 2017 5,093,442 ​ 15.32 7.62 ​ $ 35,495 ​ Options granted 1,805,937 ​ ​ 27.43 ​ ​ ​ ​ ​ ​ Options forfeited (107,720) ​ ​ 21.66 ​ ​ ​ ​ ​ ​ Options exercised(3) (824,731) ​ ​ 9.24 ​ ​ ​ ​ ​ ​ Balances at December 31, 2018 5,966,928 ​ 19.71 7.51 ​ $ 99,273 ​ Options granted 2,142,228 ​ ​ 35.80 ​ ​ ​ ​ ​ ​ Options forfeited (390,950) ​ ​ 32.23 ​ ​ ​ ​ ​ ​ Options exercised(3) (543,887) ​ ​ 17.04 ​ ​ ​ ​ ​ ​ Balances at December 31, 2019 7,174,319 ​ $ 24.03 ​ 7.32 ​ $ 79,116 ​ As of December 31, 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options vested and expected to vest 7,174,319 ​ $ 24.03 7.32 ​ $ 79,116 ​ Exercisable 3,950,965 ​ $ 17.79 6.17 ​ $ 66,286 ​
Schedule of stock options outstanding and exercisable by exercise price	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock Options Outstanding ​ Stock Options Exercisable ​ ​ ​ ​ Weighted- ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Remaining Weighted- ​ Weighted- Range of ​ ​ ​ Contractual ​ Average ​ ​ ​ Average Exercise ​ Number of ​ Term ​ Exercise Price ​ Number of ​ Exercise Price Prices ​ Shares ​ (in years) ​ Per Share ​ Shares ​ Per Share $0.59 – $4.25 238,621 3.45 ​ $ 3.49 238,621 ​ $ 3.49 ​ $10.28 – $15.51 1,378,151 5.37 ​ $ 12.21 1,350,781 ​ $ 12.19 ​ $15.69 – $23.75 2,878,221 7.04 ​ $ 21.37 1,963,376 ​ $ 20.62 ​ $23.80 – $35.80 ​ 1,071,704 ​ 8.66 ​ $ 31.18 ​ 276,042 ​ $ 27.64 ​ $36.03 – $44.19 ​ 1,607,622 ​ 9.16 ​ $ 37.22 ​ 122,145 ​ $ 39.85 ​ ​ 7,174,319 7.32 ​ $ 24.03 3,950,965 ​ $ 17.79 ​
Schedule of weighted average assumptions used for estimation of fair value of stock options	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options ​ ​ 2019 2018 2017 Common stock fair value per share ​ $ 17.37 - 25.14 ​ $ 21.80 - 43.16 ​ $ 19.61 - 25.67 ​ Expected volatility ​ 60.67% - 61.33% ​ 70.97% - 73.10% ​ 77.42% - 96.73% ​ Risk-free interest rate ​ 1.37% - 2.60% ​ 2.29% - 3.10% ​ 0.96% - 2.37% ​ Expected dividend yield ​ — ​ — ​ — ​ Expected term (in years) ​ 5.23 - 6.59 ​ 5.23 - 6.08 ​ 5.23 - 6.08 ​
Schedule of weighted average assumptions used for estimation of fair value of ESPP	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ESPP ​ ​ 2019 2018 2017 ​ Expected term (years) 0.5 - 2.0 0.5 - 2.0 0.5 - 2.0 ​ Expected volatility ​ 50.77% - 71.37% ​ 57.04% - 71.37% ​ 67.83% - 79.76% ​ Risk-free interest rate 1.47% - 2.70% ​ 1.47% - 2.70% ​ 0.47% - 1.80% ​ Expected dividend yield ​ — ​ — ​ — ​
Summary of restricted stock unity activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted- ​ ​ ​ ​ Average ​ ​ ​ ​ Grant Date ​ ​ Number of ​ Fair Value ​ ​ Shares ​ (Per Unit) Unvested at December 31, 2018 33,933 ​ $ 27.64 Granted 71,566 ​ ​ 36.68 Vested (11,311) ​ ​ 27.64 Forfeited ​ (4,182) ​ ​ 31.12 Unvested at December 31, 2019 90,006 ​ $ 34.66

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2019
Leases
Schedule of operating lease liabilities maturities	The following table reconciles the undiscounted cash flows for the operating leases at December 31, 2019 to the operating lease liabilities recorded on the balance sheet (in thousands): ​ ​ ​ ​ Years ending December 31, ​ ​ 2020 ​ $ 2,703 2021 ​ ​ 2,588 2022 ​ ​ 2,208 2023 ​ ​ 1,352 2024 ​ ​ 1,371 Thereafter ​ ​ 2,282 Total undiscounted lease payments ​ ​ 12,504 Less: Imputed interest ​ ​ (1,770) Present value of lease payments ​ $ 10,734 ​ ​ ​ ​ Lease liabilities - short-term ​ $ 2,169 Lease liabilities - long-term ​ ​ 8,565 Total lease liabilities ​ $ 10,734

Collaboration and Licensing A_2

Collaboration and Licensing Agreements (Tables)	12 Months Ended
	Dec. 31, 2019
Collaboration and Licensing Agreements
Schedule of revenue by licensees	The $156.7 million, $40.6 million and $46.2 million of revenue recorded for the years ended December 31, 2019, 2018 and 2017, respectively, were earned principally from the following licensees (in millions): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2019 ​ 2018 ​ 2017 Amgen $ 5.0 $ 0.6 $ 10.0 ​ Alexion ​ ​ 13.0 ​ 20.0 ​ — ​ Astellas ​ ​ 14.0 ​ — ​ — ​ CSL ​ ​ — ​ — ​ 3.5 ​ Genentech ​ ​ 113.9 ​ — ​ — ​ MorphoSys ​ ​ — ​ — ​ 12.5 ​ Novartis ​ ​ 10.0 ​ ​ 20.0 ​ ​ 20.1 ​ Other ​ ​ 0.8 ​ — ​ 0.1 ​ Total ​ $ 156.7 ​ $ 40.6 ​ $ 46.2 ​ The below table summarizes the disaggregation of revenue recorded for the years ended December 31, 2019, 2018 and 2017 (in millions): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2019 ​ 2018 ​ 2017 Research collaboration $ 16.3 $ 20.1 $ 20.1 Milestone ​ ​ 23.2 ​ 20.5 ​ 26.0 Licensing ​ ​ 112.2 ​ — ​ 0.1 Royalties ​ ​ 5.0 ​ — ​ — Total ​ $ 156.7 ​ $ 40.6 ​ $ 46.2
Schedule of disaggregation of revenue	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2019 ​ 2018 ​ 2017 Amgen $ 5.0 $ 0.6 $ 10.0 ​ Alexion ​ ​ 13.0 ​ 20.0 ​ — ​ Astellas ​ ​ 14.0 ​ — ​ — ​ CSL ​ ​ — ​ — ​ 3.5 ​ Genentech ​ ​ 113.9 ​ — ​ — ​ MorphoSys ​ ​ — ​ — ​ 12.5 ​ Novartis ​ ​ 10.0 ​ ​ 20.0 ​ ​ 20.1 ​ Other ​ ​ 0.8 ​ — ​ 0.1 ​ Total ​ $ 156.7 ​ $ 40.6 ​ $ 46.2 ​
Schedule of revenue from U.S. and Non U.S. sources	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year Ended ​ ​ December 31, ​ ​ 2019 ​ 2018 ​ 2017 U.S. Revenue $ 142.7 $ 40.6 $ 30.2 ​ Non-U.S. Revenue ​ ​ 14.0 ​ ​ — ​ ​ 16.0 ​ Total ​ $ 156.7 ​ $ 40.6 ​ $ 46.2 ​

Condensed Quarterly Financial_2

Condensed Quarterly Financial Data (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2019
Condensed Quarterly Financial Data (unaudited)
Schedule of Quarterly Financial Data	Quarterly Financial Data (in thousands, except per share data): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 Quarter Ended ​ March 31, June 30, September 30, December 31, Total revenue ​ $ 111,939 ​ $ 19,485 ​ $ 21,760 ​ $ 3,516 ​ Income (loss) from operations ​ 78,244 ​ (19,572) ​ (14,276) ​ (30,572) ​ Net income (loss) ​ 80,045 ​ (16,034) ​ (10,224) ​ (26,912) ​ Basic net income (loss) per common share ​ 1.42 ​ (0.28) ​ (0.18) ​ (0.47) ​ Diluted net income (loss) per common share ​ ​ 1.38 ​ ​ (0.28) ​ ​ (0.18) ​ ​ (0.47) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2018 Quarter Ended ​ ​ March 31, ​ June 30, ​ September 30, ​ December 31, Total revenue $ — ​ $ — ​ $ 29,039 ​ $ 11,564 ​ Income (loss) from operations ​ (30,649) ​ (28,290) ​ 651 ​ (21,082) ​ Net income (loss) ​ (29,493) ​ (25,869) ​ 3,150 ​ (18,197) ​ Basic net income (loss) per common share ​ (0.62) ​ (0.46) ​ 0.06 ​ (0.32) ​ Diluted net income (loss) per common share ​ ​ (0.62) ​ ​ (0.46) ​ ​ 0.05 ​ ​ (0.32) ​

Summary of Significant Accoun_4

Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Lease liability	$ 10,734
Right-of-Use Asset	9,380
Increase in assets	670,250		576,732
Increase in liabilities	77,049		55,051
Impact on retained earnings (accumulated deficit)	$ (296,402)		$ (323,277)
ASU 2016-02 | Restatement Adjustment
Lease liability		$ 12,700
Right-of-Use Asset		$ 11,400

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Concentration Risk (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)customer	Dec. 31, 2018USD ($)customer
Concentrations of risk
Deferred revenue	$ 47.1	$ 40.1
Accrued interest	2.7	2.3
Amounts on deposit in excess of federally insured limits approximately	$ 50	$ 26
Payables | Service providers or vendors
Concentrations of risk
Number of service providers | customer	2	4
Concentration risk percentage	48.00%	49.00%
Number of critical suppliers | customer	3

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value of Financial Instruments
Money Market Funds	$ 50,312	$ 26,246
Securities	550,996
Money Market Funds
Fair Value of Financial Instruments
Money Market Funds	32,009	18,270
Corporate Securities
Fair Value of Financial Instruments
Securities	281,751	104,967
Government Securities
Fair Value of Financial Instruments
Securities	269,245	399,256
Fair Value, Measurements, Recurring
Fair Value of Financial Instruments
Total Fair Value	583,005	522,493
Fair Value, Measurements, Recurring | Money Market Funds
Fair Value of Financial Instruments
Money Market Funds	32,009	18,270
Fair Value, Measurements, Recurring | Corporate Securities
Fair Value of Financial Instruments
Securities	281,751	104,967
Fair Value, Measurements, Recurring | Government Securities
Fair Value of Financial Instruments
Securities	269,245	399,256
Level 1 | Fair Value, Measurements, Recurring
Fair Value of Financial Instruments
Total Fair Value	32,009	18,270
Level 1 | Fair Value, Measurements, Recurring | Money Market Funds
Fair Value of Financial Instruments
Money Market Funds	32,009	18,270
Level 2 | Fair Value, Measurements, Recurring
Fair Value of Financial Instruments
Total Fair Value	550,996	504,223
Level 2 | Fair Value, Measurements, Recurring | Corporate Securities
Fair Value of Financial Instruments
Securities	281,751	104,967
Level 2 | Fair Value, Measurements, Recurring | Government Securities
Fair Value of Financial Instruments
Securities	$ 269,245	$ 399,256

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Property, Plant, and Equipment (Details)	12 Months Ended
	Dec. 31, 2019
Computers, software and equipment | Minimum
Property and Equipment
Estimated useful lives of the assets	3 years
Computers, software and equipment | Maximum
Property and Equipment
Estimated useful lives of the assets	5 years
Furniture and fixtures | Minimum
Property and Equipment
Estimated useful lives of the assets	5 years
Furniture and fixtures | Maximum
Property and Equipment
Estimated useful lives of the assets	7 years
Leasehold improvements | Minimum
Property and Equipment
Estimated useful lives of the assets	5 years
Leasehold improvements | Maximum
Property and Equipment
Estimated useful lives of the assets	7 years

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Intangibles (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)item	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Patents, licenses, and other intangible assets
Number of primary criteria to determine capitalization of patent | item	3
Abandonment costs	$ 221	$ 239	$ 396
Total gross carrying amount	20,772	17,374
Total intangible assets, net	14,421	11,969
Amortization expense for patents, licenses, and other intangible assets	900	900	$ 800
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2020	1,009
2021	912
2022	880
2023	809
2024	647
Thereafter	2,365
Total	6,622
Nonamortizable intangible assets (trademarks)
Patents, licenses, and other intangible assets
Nonamortizable intangible assets (trademarks)	$ 399	399
Acquired licenses | Minimum
Patents, licenses, and other intangible assets
Estimated economic life	5 years
Acquired licenses | Maximum
Patents, licenses, and other intangible assets
Estimated economic life	25 years
Patents
Patents, licenses, and other intangible assets
Accumulated amortization	$ (4,912)	(4,142)
Patents | Minimum
Patents, licenses, and other intangible assets
Estimated economic life	13 years
Patents | Maximum
Patents, licenses, and other intangible assets
Estimated economic life	20 years
Patents, definite life
Patents, licenses, and other intangible assets
Amortizable intangible assets	$ 10,597	9,320
Patents, pending issuance
Patents, licenses, and other intangible assets
Amortizable intangible assets	7,266	5,644
Licenses and other amortizable intangible assets
Patents, licenses, and other intangible assets
Amortizable intangible assets	2,510	2,011
Accumulated amortization	(1,439)	$ (1,263)
In-process intangible assets
Patents, licenses, and other intangible assets
Total gross carrying amount	$ 7,300

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
US corporate tax rate	35.00%	21.00%	21.00%
Federal
Income Taxes [Line Items]
Income tax receivable		$ 0.8	$ 1.6

Summary of Significant Accou_10

Summary of Significant Accounting Policies - Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock-Based Compensation
Stock-based compensation expense									$ 31,851	$ 20,548	$ 13,651
Basic numerator:
Net income (loss) attributable to common stockholders									$ 26,875	$ (70,409)	$ (38,486)
Denominator:
Weighted average common shares outstanding, basic									56,531,439	53,942,116	46,817,756
Net income (loss) per common share, basic (in dollars per share)	$ (0.47)	$ (0.18)	$ (0.28)	$ 1.42	$ (0.32)	$ 0.06	$ (0.46)	$ (0.62)	$ 0.48	$ (1.31)	$ (0.82)
Diluted numerator:
Net income (loss) attributable to common stockholders for diluted net income (loss) per share									$ 26,875	$ (70,409)	$ (38,486)
Denominator
Weighted average common shares outstanding, basic									56,531,439	53,942,116	46,817,756
Dilutive effect of employee stock options and ESPP									1,936,441
Weighted average common shares outstanding, diluted									58,467,880	53,942,116	46,817,756
Net income (loss) per common share, diluted (in dollars per share)	$ (0.47)	$ (0.18)	$ (0.28)	$ 1.38	$ (0.32)	$ 0.05	$ (0.46)	$ (0.62)	$ 0.46	$ (1.31)	$ (0.82)
Employee stock options
Net Income (Loss) Per Share
Securities excluded in calculation of EPS									1,022,623
Net Loss Per Share
Securities included in calculation of EPS									1,923,310
Securities excluded in calculation of EPS									1,022,623
ESPP
Stock-Based Compensation
Stock-based compensation expense									$ 700	$ 700	$ 500
Employee stock options
Stock-Based Compensation
Stock-based compensation expense									30,502	19,537	$ 13,153
Restricted stock units
Stock-Based Compensation
Stock-based compensation expense									$ 662	$ 267
Net Loss Per Share
Securities included in calculation of EPS									13,131

Summary of Significant Accou_11

Summary of Significant Accounting Policies - Segments (Details)	12 Months Ended
	Dec. 31, 2019segment
Segment Reporting
Number of Operating Segments	1

Marketable Securities (Details)

Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities
Cash and cash equivalents	$ 50,312	$ 26,246
Investments, amortized cost	581,834	523,454
Investments	583,005	522,493
Total amortized cost	549,825
Gross unrealized gains	1,201	188
Gross unrealized losses	(30)	(1,149)
Securities	550,996
Marketable securities
Schedule of Available-for-sale Securities
Securities	550,996	504,223
Money Market Funds
Schedule of Available-for-sale Securities
Cash and cash equivalents	32,009	18,270
Corporate Securities
Schedule of Available-for-sale Securities
Total amortized cost	281,586	105,311
Gross unrealized gains	195	1
Gross unrealized losses	(30)	(345)
Securities	281,751	104,967
Government Securities
Schedule of Available-for-sale Securities
Total amortized cost	268,239	399,873
Gross unrealized gains	1,006	187
Gross unrealized losses		(804)
Securities	269,245	399,256
Cash and Cash Equivalents
Schedule of Available-for-sale Securities
Cash and cash equivalents	$ 32,009	$ 18,270

Marketable Securities - Maturit

Marketable Securities - Maturities (Details) $ in Thousands	Dec. 31, 2019USD ($)
Amortized Cost
Maturing in one year or less	$ 478,338
Maturing within two years	71,487
Total amortized cost	549,825
Estimate Fair Value
Maturing in one year or less	479,470
Maturing within two years	71,526
Total estimated fair value	$ 550,996

Marketable Securities - Unreali

Marketable Securities - Unrealized losses (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair value
Fair value, less than 12 months	$ 46,303	$ 260,891
Fair value, 12 months or greater	13,992	134,635
Unrealized losses
Unrealized losses, Less than 12 months	(24)	(982)
Unrealized gain (losses), 12 months or greater	(6)	(167)
Corporate Securities
Fair value
Fair value, less than 12 months	46,303	84,666
Fair value, 12 months or greater	13,992	17,805
Unrealized losses
Unrealized losses, Less than 12 months	(24)	(310)
Unrealized gain (losses), 12 months or greater	$ (6)	(35)
Government Securities
Fair value
Fair value, less than 12 months		176,225
Fair value, 12 months or greater		116,830
Unrealized losses
Unrealized losses, Less than 12 months		(672)
Unrealized gain (losses), 12 months or greater		$ (132)

Sale of Additional Common Sto_2

Sale of Additional Common Stock (Details) - USD ($) $ in Thousands	Sep. 19, 2016	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Proceeds from sale of common stock			$ 245,504	$ 2,797
Common Stock
Sale of common stock		8,395,000	8,395,000	363,603
Proceeds from sale of common stock		$ 245,500	$ 84	$ 4
Piper Jaffray | Common Stock | Maximum
Net proceeds	$ 40,000

Property and Equipment (Details

Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property and equipment
Property and equipment, gross	$ 28,410	$ 21,239
Less accumulated depreciation and amortization	(12,605)	(9,426)
Property and equipment, net	15,805	11,813
Depreciation and amortization expense	3,400	2,400	$ 1,200
Computers, software and equipment
Property and equipment
Property and equipment, gross	21,087	16,292
Furniture and fixtures
Property and equipment
Property and equipment, gross	492	173
Leasehold and tenant improvements
Property and equipment
Property and equipment, gross	$ 6,831	$ 4,774

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of federal statutory income tax to effective income tax
Current tax expense	$ 300
Federal statutory income tax rate	5,709	$ (14,795)	$ (13,243)
State and local income taxes	2,549	(4,767)	(1,806)
Research and development credit	(6,747)	(6,170)	(5,554)
Stock based compensation	1,927	444	2,709
Effect of the 2017 Tax Cuts and Jobs Act			19,596
State Credit	1,725
Other	(301)	414	720
Net change in valuation allowance	(4,550)	24,874	(2,885)
Income tax provision (benefit)	$ 312	$ 0	$ (463)

Income Taxes - Deferred tax ass

Income Taxes - Deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred income tax assets
Net operating loss carryforwards	$ 36,891	$ 49,889
Research credits	28,415	23,151
Depreciation	334	207
Unrealized loss on securities		269
Accrued compensation	4,788	1,097
Deferred revenue	11,215	11,222
State taxes	64
Gross deferred income tax assets	81,707	85,835
Valuation allowance	(77,389)	(82,537)
Net deferred income tax assets	4,318	3,298
Deferred income tax liabilities
Patent costs	(3,736)	(3,142)
Licensing costs	(229)	(125)
Capitalized legal costs	(26)	(31)
Unrealized gain on securities	(327)
Gross deferred income tax liabilities	$ (4,318)	$ (3,298)

Income Taxes - TCJA and Net ope

Income Taxes - TCJA and Net operating loss carryforwards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Increase (decrease) in deferred tax asset valuation allowance	$ (5,100)
Federal
Income Taxes [Line Items]
Income tax receivable	800	$ 1,600
Cumulative net operating loss carryforwards	144,700
Tax credit carryforwards	19,700
Tax credits expired amount	30
Tax credits expiring in next five years	300
State
Income Taxes [Line Items]
Cumulative net operating loss carryforwards	92,800
Tax credit carryforwards	11,000
Years Prior to 2018 | Federal
Income Taxes [Line Items]
Cumulative net operating loss carryforwards	$ 68,000
Percentage of net operating losses which can offset future taxable income	100.00%
Tax Year 2018 | Federal
Income Taxes [Line Items]
Cumulative net operating loss carryforwards	$ 76,700
Percentage of net operating losses which can offset future taxable income	80.00%

Stock-Based Compensation - Plan

Stock-Based Compensation - Plan details (Details)	Jan. 01, 2018shares	Jan. 01, 2014shares	Dec. 31, 2019item$ / sharesshares	Dec. 31, 2018$ / sharesshares	Dec. 31, 2017$ / sharesshares	Dec. 31, 2016shares	Dec. 31, 2015shares
Stock options
Stock-based compensation
Total number of shares of common stock available for issuance			3,975,160	3,576,574	3,394,691
Options granted (in shares)			2,142,228	1,805,937
Information with respect to stock options outstanding
Exercisable options (in shares)			3,950,965	3,058,659	2,558,941
Weighted-average exercise price per share of exercisable options (in dollars per share) | $ / shares			$ 17.79	$ 15.12	$ 11.06
Weighted average grant date fair value per share of options granted during the year (in dollars per share) | $ / shares			$ 20.74	$ 18.06	$ 16.92
Weighted-average remaining contractual life			7 years 3 months 25 days	7 years 6 months 3 days	7 years 7 months 13 days
ESPP
Stock-based compensation
Total number of shares of common stock available for issuance			581,286
Initial term of plan			2 years
Second term of plan			2 years
Number of six month purchase periods | item			4
Purchase period			6 months
Increase in shares of common stock available for issuance (in shares)		313,545		0	0	0	0
Awards issued under the plan (in shares)			417,277
ESPP | Minimum
Stock-based compensation
Percentage of compensation that employees may withhold to purchase stock at a discount			1.00%
ESPP | Maximum
Stock-based compensation
Percentage of compensation that employees may withhold to purchase stock at a discount			15.00%
Purchase price as percentage of stock price at the initial offering date			85.00%
Purchase price as percentage of stock price at the purchase date			85.00%
Annual percentage increase in shares of common stock available for issuance			1.00%
Annual increase in shares of common stock available for issuance (in shares)			621,814
Restricted stock units
Stock-based compensation
Restricted stock granted (in shares)			71,566
The 2010 Plan
Stock-based compensation
Total number of shares of common stock available for issuance			0
The 2013 Plan
Stock-based compensation
Total number of shares of common stock available for issuance			11,277,816
Annual percentage increase in shares of common stock available for issuance			4.00%
Increase in shares of common stock available for issuance (in shares)	2,251,181
Awards issued under the plan (in shares)			8,893,515
The 2013 Plan | Restricted stock units
Stock-based compensation
Restricted stock granted (in shares)			105,499
Annual installment vesting periods | item			3

Stock-Based Compensation - Empl

Stock-Based Compensation - Employee expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	$ 31,851	$ 20,548	$ 13,651
Employee stock options
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	30,502	19,537	13,153
ESPP
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	687	744	498
Restricted stock units
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	662	267
General and administrative
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	8,854	7,699	5,617
Research and development
Stock-based compensation
Total employee, director and non-employee stock-based compensation expense	$ 22,997	$ 12,849	$ 8,034

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Option Activity (Details) - Stock options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock option activity, Number of Shares
Balance at the beginning of the period (in shares)	5,966,928	5,093,442
Options granted (in shares)	2,142,228	1,805,937
Options forfeited (in shares)	(390,950)	(107,720)
Options exercised (in shares)	(543,887)	(824,731)
Balance at the end of the period (in shares)	7,174,319	5,966,928	5,093,442
Options vested and expected to vest (in shares)	7,174,319
Exercisable (in shares)	3,950,965	3,058,659	2,558,941
Weighted Average Exercise Price (Per Share)
Balance at the beginning of the period (in dollars per share)	$ 19.71	$ 15.32
Options granted (in dollars per share)	35.80	27.43
Options forfeited (in dollars per share)	32.23	21.66
Options exercised (in dollars per share)	17.04	9.24
Balance at the end of the period (in dollars per share)	24.03	19.71	$ 15.32
Options vested and expected to vest (in dollars per share)	24.03
Exercisable (in dollars per share)	$ 17.79	$ 15.12	$ 11.06
Additional information
Weighted-Average Remaining Contractual Term, Balance outstanding	7 years 3 months 25 days	7 years 6 months 3 days	7 years 7 months 13 days
Weighted-Average Remaining Contractual Term, Options vested and expected to vest	7 years 3 months 25 days
Weighted-Average Remaining Contractual Term, Exercisable	6 years 2 months 1 day
Aggregate Intrinsic Value, Balance outstanding	$ 79,116	$ 99,273	$ 35,495
Aggregate Intrinsic Value, Options vested and expected to vest	79,116
Aggregate Intrinsic Value, Exercisable	66,286
Intrinsic value of options exercised	$ 11,500	$ 23,600	$ 5,700

Stock-Based Compensation - Opti

Stock-Based Compensation - Options by exercise price (Details)	12 Months Ended
	Dec. 31, 2019$ / sharesshares
Stock options outstanding and exercisable by exercise price
Stock Options Outstanding, Number of Shares | shares	7,174,319
Stock Options Outstanding, Remaining Contractual Term	7 years 3 months 25 days
Stock Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 24.03
Stock Options Exercisable, Number of Shares | shares	3,950,965
Stock Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 17.79
$0.59 - $4.25
Stock options outstanding and exercisable by exercise price
Range of Exercise Prices, lower limit (in dollars per share)	0.59
Range of Exercise Prices, upper limit (in dollars per share)	$ 4.25
Stock Options Outstanding, Number of Shares | shares	238,621
Stock Options Outstanding, Remaining Contractual Term	3 years 5 months 12 days
Stock Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 3.49
Stock Options Exercisable, Number of Shares | shares	238,621
Stock Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 3.49
$9.78 - $14.75
Stock options outstanding and exercisable by exercise price
Range of Exercise Prices, lower limit (in dollars per share)	10.28
Range of Exercise Prices, upper limit (in dollars per share)	$ 15.51
Stock Options Outstanding, Number of Shares | shares	1,378,151
Stock Options Outstanding, Remaining Contractual Term	5 years 4 months 13 days
Stock Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 12.21
Stock Options Exercisable, Number of Shares | shares	1,350,781
Stock Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 12.19
$14.77 - $22.18
Stock options outstanding and exercisable by exercise price
Range of Exercise Prices, lower limit (in dollars per share)	15.69
Range of Exercise Prices, upper limit (in dollars per share)	$ 23.75
Stock Options Outstanding, Number of Shares | shares	2,878,221
Stock Options Outstanding, Remaining Contractual Term	7 years 14 days
Stock Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 21.37
Stock Options Exercisable, Number of Shares | shares	1,963,376
Stock Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 20.62
$22.20 - $33.78
Stock options outstanding and exercisable by exercise price
Range of Exercise Prices, lower limit (in dollars per share)	23.80
Range of Exercise Prices, upper limit (in dollars per share)	$ 35.80
Stock Options Outstanding, Number of Shares | shares	1,071,704
Stock Options Outstanding, Remaining Contractual Term	8 years 7 months 28 days
Stock Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 31.18
Stock Options Exercisable, Number of Shares | shares	276,042
Stock Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 27.64
$34.56 - $43.16
Stock options outstanding and exercisable by exercise price
Range of Exercise Prices, lower limit (in dollars per share)	36.03
Range of Exercise Prices, upper limit (in dollars per share)	$ 44.19
Stock Options Outstanding, Number of Shares | shares	1,607,622
Stock Options Outstanding, Remaining Contractual Term	9 years 1 month 28 days
Stock Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 37.22
Stock Options Exercisable, Number of Shares | shares	122,145
Stock Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 39.85

Stock-Based Compensation - FV o

Stock-Based Compensation - FV of employee stock options (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee stock options
Weighted average assumptions for estimated fair value of employee stock options
Common stock fair value per share minimum	17.37	21.80	19.61
Common stock fair value per share maximum	25.14	43.16	25.67
Expected volatility, low end of range (as a percent)	60.67%	70.97%	77.42%
Expected volatility, high end of range (as a percent)	61.33%	73.10%	96.73%
Risk-free interest rate, low end of range (as a percent)	1.37%	2.29%	0.96%
Risk-free interest rate, high end of range (as a percent)	2.60%	3.10%	2.37%
Compensation expense
Unamortized compensation expense related to unvested options	$ 51.1	$ 42.8
Period to recognize unamortized compensation expense	2 years 8 months 19 days
Employee stock options | Minimum
Weighted average assumptions for estimated fair value of employee stock options
Expected term (years)	5 years 2 months 23 days	5 years 2 months 23 days	5 years 2 months 23 days
Employee stock options | Maximum
Weighted average assumptions for estimated fair value of employee stock options
Expected term (years)	6 years 7 months 2 days	6 years 29 days	6 years 29 days
ESPP
Weighted average assumptions for estimated fair value of employee stock options
Expected volatility, low end of range (as a percent)	50.77%	57.04%	67.83%
Expected volatility, high end of range (as a percent)	71.37%	71.37%	79.76%
Risk-free interest rate, low end of range (as a percent)	1.47%	1.47%	0.47%
Risk-free interest rate, high end of range (as a percent)	2.70%	2.70%	1.80%
Compensation expense
Unamortized compensation expense related to unvested options	$ 1.4	$ 0.8
Period to recognize unamortized compensation expense	1 month 28 days
ESPP | Minimum
Weighted average assumptions for estimated fair value of employee stock options
Expected term (years)	6 months	6 months	6 months
ESPP | Maximum
Weighted average assumptions for estimated fair value of employee stock options
Expected term (years)	2 years	2 years	2 years

Stock Based Compensation - Rest

Stock Based Compensation - Restricted stock units (Details) - Restricted stock units - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Stock-based compensation
Beginning balance	33,933
Granted	71,566
Vested	(11,311)
Forfeited	(4,182)
Ending balance	90,006
Weighted Average Grant Date Fair Value, Beginning Balance	$ 27.64
Weighted Average Grant Date Fair Value, Granted	36.68
Weighted Average Grant Date Fair Value, Vested	27.64
Weighted Average Grant Date Fair Value, Forfeited	31.12
Weighted Average Grant Date Fair Value, Ending Balance	$ 34.66
Compensation expense
Unamortized compensation expense related to unvested restricted stock units	$ 2.5	$ 0.7
Period to recognize unamortized compensation expense	2 years 5 months 4 days

Leases (Details)

Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Jul. 31, 2019
Lessee, Lease, Description [Line Items]
Option to extend	true
2020	$ 2,703
2021	2,588
2022	2,208
2023	1,352
2024	1,371
Thereafter	2,282
Total undiscounted lease payments	12,504
Less: Imputed interest	(1,770)
Present value of lease payments	$ 10,734
Monrovia, CA - office and laboratory space
Lessee, Lease, Description [Line Items]
Renewal term	5 years
Monrovia, CA - office and laboratory space with additional space
Lessee, Lease, Description [Line Items]
Renewal term		5 years
San Diego, CA - office space
Lessee, Lease, Description [Line Items]
Renewal term	5 years
San Diego, CA - second office space
Lessee, Lease, Description [Line Items]
Renewal term	5 years

Leases - Operating lease liabil

Leases - Operating lease liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Leases
Lease liability - short-term	$ 2,169
Lease liability - long-term	8,565
Operating lease liabilities	10,734
Operating lease cost	2,700
Cash paid for operating leases	$ 2,600
Net rent expense		$ 2,500
Remaining lease term	5 years 6 months
Discount rate	5.50%

Collaboration and Licensing A_3

Collaboration and Licensing Agreements (Details)	Mar. 29, 2019USD ($)	Dec. 31, 2019USD ($)	Nov. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)companyitem	Feb. 28, 2019	Oct. 31, 2017USD ($)shares	Mar. 31, 2017USD ($)	Jun. 30, 2016item	Sep. 30, 2015USD ($)item	Jan. 31, 2013item	Jun. 30, 2010USD ($)	Feb. 28, 2009item	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)item	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)item	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Jul. 31, 2016USD ($)
Collaboration research and licensing agreements
Deferred revenue		$ 47,100,000												$ 47,100,000				$ 40,100,000				$ 47,100,000	$ 40,100,000
Revenue recorded														3,516,000	$ 21,760,000	$ 19,485,000	$ 111,939,000	11,564,000	$ 29,039,000			156,700,000	40,603,000	$ 46,150,000
Current portion of deferred revenue		45,205,000												45,205,000				40,079,000				45,205,000	40,079,000
Non Current portion of deferred revenue		1,926,000												1,926,000								1,926,000
Licensing
Collaboration research and licensing agreements
Revenue recorded																						112,200,000		100,000
Royalty
Collaboration research and licensing agreements
Revenue recorded																						5,000,000
Milestone
Collaboration research and licensing agreements
Revenue recorded																						23,200,000	20,500,000	26,000,000
Genentech
Collaboration research and licensing agreements
Revenue recorded																						113,900,000
Astellas
Collaboration research and licensing agreements
Nonrefundable upfront payment	$ 15,000,000
Revenue recorded																						$ 14,000,000
Novartis
Collaboration research and licensing agreements
Number of performance obligations | item																						2
Revenue recorded																						$ 10,000,000	20,000,000	20,100,000
Amgen, Inc.
Collaboration research and licensing agreements
Revenue recorded																						5,000,000	600,000	10,000,000
MorphoSys
Collaboration research and licensing agreements
Revenue recorded																								12,500,000
Alexion
Collaboration research and licensing agreements
Revenue recorded																						13,000,000	20,000,000
CSL Limited
Collaboration research and licensing agreements
Revenue recorded																								3,500,000
Other [Member]
Collaboration research and licensing agreements
Revenue recorded																						800,000		100,000
2009 Research License and Commercialization Agreement | CSL Limited
Collaboration research and licensing agreements
Revenue recognized								$ 3,500,000														0	0	3,500,000
Deferred revenue		0												0								0
Number of commercial licenses | item													1
Collaboration and License Agreement | Genentech
Collaboration research and licensing agreements
Performance obligation					$ 120,000,000												120,000,000
Nonrefundable upfront payment					$ 120,000,000
Percentage of profits on net sales of the product					45.00%	45.00%
Research license term					2 years
Revenue recognized																						$ 113,900,000
Number of companies that conduct integrated research plan | company					2
Number of programs | item					9
Term of revenue recognized																						1 year
Collaboration and License Agreement | Genentech | XmAb24306
Collaboration research and licensing agreements
Performance obligation					$ 111,700,000												111,700,000
Cost sharing receivable (payable)		900,000												900,000								$ 900,000
Collaboration and License Agreement | Genentech | Research service
Collaboration research and licensing agreements
Performance obligation					8,300,000												8,300,000
Revenue recognized																						2,200,000
Deferred revenue		6,100,000												6,100,000								6,100,000
Collaboration and License Agreement | Genentech | Licensing
Collaboration research and licensing agreements
Revenue recognized					111,700,000
Collaboration and License Agreement | Genentech | Maximum
Collaboration research and licensing agreements
Potential milestone payment					160,000,000												160,000,000
Collaboration and License Agreement | Genentech | Cost approach | Research service
Collaboration research and licensing agreements
Standalone selling price					8,500,000												8,500,000
Collaboration and License Agreement | Genentech | Cost approach | Licensing
Collaboration research and licensing agreements
Standalone selling price					114,400,000												114,400,000
Collaboration and License Agreement | Genentech | Collaboration Products
Collaboration research and licensing agreements
Performance obligation		0												0								0
Collaboration and License Agreement | Novartis
Collaboration research and licensing agreements
Performance obligation		160,000,000												160,000,000								160,000,000			$ 150,000,000
Revenue recognized																						10,000,000	20,000,000	20,100,000
Contract receivable		12,200,000												12,200,000								12,200,000
Deferred revenue		40,100,000												40,100,000								$ 40,100,000
Remaining cost sharing settlement amount			$ 1,400,000
Collaboration and License Agreement | Novartis | Discovery Program
Collaboration research and licensing agreements
Right to substitute identified target period																						5 years
Collaboration and License Agreement | Novartis | Bispecific FC Technologies
Collaboration research and licensing agreements
Research license term									5 years
Number of development stage products | item									2
Number of previously identified products | item									4
Collaboration and License Agreement | Novartis | Bispecific FC Technologies | XmAb14045
Collaboration research and licensing agreements
Performance obligation		27,100,000												27,100,000								$ 27,100,000
Collaboration and License Agreement | Novartis | Bispecific FC Technologies | XmAb13676
Collaboration research and licensing agreements
Performance obligation		31,400,000												31,400,000								31,400,000
Collaboration and License Agreement | Novartis | Bispecific FC Technologies | Maximum
Collaboration research and licensing agreements
Number of drug candidates | item									4
Number of antibody targets for which bispecific technology applied | item									4
Collaboration and License Agreement | Novartis | Global Discovery Program
Collaboration research and licensing agreements
Performance obligation		90,200,000												90,200,000								$ 90,200,000
Proceeds from milestone payments		10,000,000
Revenue recognized															10,000,000				20,000,000					20,100,000
Number of programs | item									4													4
Collaboration and License Agreement | Novartis | Global Discovery Program | Maximum
Collaboration research and licensing agreements
Number of antibody targets for which bispecific technology applied | item									4
Collaboration and License Agreement | Novartis | FC Licenses
Collaboration research and licensing agreements
Performance obligation		11,300,000												11,300,000								$ 11,300,000
Collaboration and License Agreement | Novartis | FC Licenses | Maximum
Collaboration research and licensing agreements
Number of targets against which non-exclusive license is provided | item									10
Collaboration and License Agreement | MorphoSys
Collaboration research and licensing agreements
Nonrefundable upfront payment												$ 13,000,000
Revenue recognized																						0	0	12,500,000
Deferred revenue		0												0								0
Research and License Agreement | Genentech | XmAb24306
Collaboration research and licensing agreements
Potential milestone payment					$ 180,000,000												$ 180,000,000
Research and License Agreement | Astellas
Collaboration research and licensing agreements
Performance obligation	15,000,000
Potential milestone payment	240,000,000
Revenue recognized																						14,000,000
Deferred revenue		1,000,000												1,000,000								1,000,000
Research and License Agreement | Astellas | Bispecific
Collaboration research and licensing agreements
Performance obligation	13,600,000
Revenue recognized				$ 13,600,000
Research and License Agreement | Astellas | Research service
Collaboration research and licensing agreements
Performance obligation	1,400,000
Research and License Agreement | Astellas | Income approach | Bispecific
Collaboration research and licensing agreements
Standalone selling price	17,100,000
Research and License Agreement | Astellas | Cost approach | Research service
Collaboration research and licensing agreements
Performance obligation	1,400,000
Standalone selling price	1,400,000
Research and License Agreement | Amgen, Inc.
Collaboration research and licensing agreements
Performance obligation		60,500,000								$ 45,000,000				60,500,000								60,500,000
Nonrefundable upfront payment										45,000,000
Potential milestone payment										600,000,000
Revenue recognized															100,000							5,000,000	600,000	10,000,000
Contract receivable		5,000,000												5,000,000								5,000,000
Deferred revenue		0												0								0
Research and License Agreement | Amgen, Inc. | Milestone
Collaboration research and licensing agreements
Proceeds from milestone payments										$ 15,500,000
Research and License Agreement | Amgen, Inc. | CD38 Program
Collaboration research and licensing agreements
Performance obligation		23,750,000												23,750,000								23,750,000
Revenue recognized																				$ 10,000,000
Research and License Agreement | Amgen, Inc. | Discovery Program
Collaboration research and licensing agreements
Performance obligation		36,750,000												36,750,000								36,750,000
Research license term										3 years
Revenue recognized															5,000,000			500,000
Number of programs | item										5
Previous targets which bispecific technology will be applied | item										5
Number of delivered discover programs | item										5
Research and License Agreement | Amgen, Inc. | Global Discovery Program
Collaboration research and licensing agreements
Number of programs | item										5
Research and License Agreement | VIR Biotechnology
Collaboration research and licensing agreements
Potential milestone payment															$ 155,250,000						$ 155,250,000
Revenue recognized																						800,000
Deferred revenue		0												0								0
Number of different target programs | item															2
Option and License Agreement | Alexion
Collaboration research and licensing agreements
Revenue recognized																		$ 11,000,000	$ 9,000,000		8,000,000	13,000,000	20,000,000	$ 0
Contract receivable		4,100,000												4,100,000								4,100,000
Deferred revenue		0												0								0
Number of different target programs | item											6
Option and License Agreement | Alexion | Royalty
Collaboration research and licensing agreements
Revenue recognized																						5,000,000
License Agreement | INmune
Collaboration research and licensing agreements
Performance obligation							$ 100,000
Nonrefundable upfront payment							$ 100,000
Revenue recognized																						0	$ 100,000
Deferred revenue		$ 0												$ 0								$ 0
Fully-diluted equity interests (as a percentage)							19.00%
Additional equity interests (as a percentage)							10.00%
Equity issued in shares | shares							1,585,000
Equity issues, value							$ 10,000,000
Development-based | Collaboration and License Agreement | Novartis | Global Discovery Program
Collaboration research and licensing agreements
Revenue recognized															$ 10,000,000
Development-based | Research and License Agreement | Astellas
Collaboration research and licensing agreements
Potential milestone payment	32,500,000
Development-based | Research and License Agreement | VIR Biotechnology
Collaboration research and licensing agreements
Potential milestone payment															5,250,000						5,250,000
Regulatory-based | Research and License Agreement | Astellas
Collaboration research and licensing agreements
Potential milestone payment	57,500,000
Regulatory-based | Research and License Agreement | VIR Biotechnology
Collaboration research and licensing agreements
Potential milestone payment															30,000,000						30,000,000
Sales-based | Research and License Agreement | Astellas
Collaboration research and licensing agreements
Potential milestone payment	$ 150,000,000
Sales-based | Research and License Agreement | VIR Biotechnology
Collaboration research and licensing agreements
Potential milestone payment															$ 120,000,000						$ 120,000,000

Collaborative and Licensing Agr

Collaborative and Licensing Agreements - Revenue Recognition (Details)	1 Months Ended	3 Months Ended						12 Months Ended
	Jun. 30, 2017USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Dec. 31, 2019USD ($)item	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded		$ 3,516,000	$ 21,760,000	$ 19,485,000	$ 111,939,000	$ 11,564,000	$ 29,039,000	$ 156,700,000	$ 40,603,000	$ 46,150,000
Deferred revenue		47,100,000				40,100,000		47,100,000	40,100,000
Current portion of deferred revenue		45,205,000				40,079,000		45,205,000	40,079,000
Non Current portion of deferred revenue		1,926,000						1,926,000
Research collaboration
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded								16,300,000	20,100,000	20,100,000
Milestone
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded								23,200,000	20,500,000	26,000,000
Licensing
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded								112,200,000		100,000
Royalty
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded								5,000,000
United States
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded								142,700,000	40,600,000	30,200,000
Non - United States
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded								14,000,000		16,000,000
Amgen, Inc.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded								5,000,000	600,000	10,000,000
Alexion
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded								13,000,000	20,000,000
Astellas
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded								14,000,000
CSL Limited
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded										3,500,000
Genentech
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded								$ 113,900,000
MorphoSys
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded										12,500,000
Novartis
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of performance obligations | item								2
Revenue recorded								$ 10,000,000	$ 20,000,000	20,100,000
Other [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recorded								800,000		$ 100,000
2009 Research License and Commercialization Agreement | CSL Limited
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue		0						$ 0
Collaboration and License Agreement | Genentech
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Term of revenue recognized								1 year
Collaboration and License Agreement | MorphoSys
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payment	$ 12,500,000
Deferred revenue		0						$ 0
Collaboration and License Agreement | Novartis
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract receivable		12,200,000						12,200,000
Deferred revenue		$ 40,100,000						$ 40,100,000

401(k) Plan (Details)

401(k) Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan employer matching contribution percent	3.50%
Employer contributions	$ 600	$ 500	$ 0
Vesting period	3 years
Annual vesting percentage	33.00%
1% of participating employee contributions
Defined Benefit Plan Disclosure [Line Items]
Percentage of company matching to defined contribution plan	100.00%
Defined contribution plan employer matching contribution percent	1.00%
5% of participating employee contributions
Defined Benefit Plan Disclosure [Line Items]
Percentage of company matching to defined contribution plan	50.00%
Defined contribution plan employer matching contribution percent	5.00%

Condensed Quarterly Financial_3

Condensed Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Quarterly Financial Data (unaudited)
Total revenue	$ 3,516	$ 21,760	$ 19,485	$ 111,939	$ 11,564	$ 29,039			$ 156,700	$ 40,603	$ 46,150
Income (loss) from operations	(30,572)	(14,276)	(19,572)	78,244	(21,082)	651	$ (28,290)	$ (30,649)	13,824	(79,370)	(43,123)
Net income (loss)	$ (26,912)	$ (10,224)	$ (16,034)	$ 80,045	$ (18,197)	$ 3,150	$ (25,869)	$ (29,493)	$ 26,875	$ (70,409)	$ (38,486)
Basic net income (loss) (in dollars per share)	$ (0.47)	$ (0.18)	$ (0.28)	$ 1.42	$ (0.32)	$ 0.06	$ (0.46)	$ (0.62)	$ 0.48	$ (1.31)	$ (0.82)
Diluted net income (loss) (in dollars per share)	$ (0.47)	$ (0.18)	$ (0.28)	$ 1.38	$ (0.32)	$ 0.05	$ (0.46)	$ (0.62)	$ 0.46	$ (1.31)	$ (0.82)

Subsequent Event (Details)

Subsequent Event (Details) - License Agreement - Subsequent Events - USD ($) $ in Millions	1 Months Ended
	Feb. 29, 2020	Jan. 31, 2020
Gilead
Collaboration research and licensing agreements
Nonrefundable upfront payment		$ 6
Aimmune
Collaboration research and licensing agreements
Nonrefundable upfront payment	$ 5
Common Stock Value receivable under License agreement	$ 5