Zogenix (ZGNX) 10-Q 6 May 20 2020 Q1 Quarterly report Financial data

Cover Page

Cover Page - shares	3 Months Ended
	Mar. 31, 2020	Apr. 30, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
Document Transition Report	false
Entity File Number	001-34962
Entity Registrant Name	ZOGENIX, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-5300780
Entity Address, Address Line One	5959 Horton Street
Entity Address, Address Line Two	Suite 500
Entity Address, City or Town	Emeryville
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94608
City Area Code	510
Local Phone Number	550-8300
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	ZGNX
Security Exchange Name	NASDAQ
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		55,340,691
Entity Central Index Key	0001375151
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 269,975	$ 62,070
Marketable securities	150,218	189,085
Other receivable	19,741	0
Prepaid expenses and other current assets	13,647	11,084
Acquisition holdback placed in escrow	25,000	25,000
Total current assets	478,581	287,239
Property and equipment, net	9,560	9,424
Operating lease right-of-use assets	8,546	7,774
Indefinite-lived intangible assets	102,500	102,500
Goodwill	6,234	6,234
Other noncurrent assets	1,485	1,079
Total assets	606,906	414,250
Current liabilities:
Accounts payable	7,887	7,979
Accrued and other current liabilities	25,803	30,117
Acquisition holdback liability	24,444	24,444
Deferred revenue, current	5,696	5,927
Current portion of operating lease liabilities	1,383	1,322
Current portion of contingent consideration	23,600	25,600
Total current liabilities	88,813	95,389
Deferred revenue, noncurrent	6,407	7,425
Operating lease liabilities, net of current portion	11,454	10,752
Contingent consideration, net of current portion	32,300	38,200
Deferred income taxes	17,425	17,425
Total liabilities	156,399	169,191
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.001 par value; 10,000 shares authorized; none issued and outstanding	0	0
Common stock, $0.001 par value; 100,000 shares authorized; and 55,341 and 45,272 shares issued and outstanding at March 31, 2020 and December 31, 2019, respectively	55	45
Additional paid-in capital	1,591,497	1,360,092
Accumulated deficit	(1,141,257)	(1,115,457)
Accumulated other comprehensive income	212	379
Total stockholders’ equity	450,507	245,059
Total liabilities and stockholders’ equity	$ 606,906	$ 414,250

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Preferred stock par value (usd per share)	$ 0.001	$ 0.001
Preferred stock authorized (shares)	10,000,000	10,000,000
Preferred stock issued (shares)	0	0
Preferred stock outstanding (shares)	0	0
Common stock par value (usd per share)	$ 0.001	$ 0.001
Common stock authorized (shares)	100,000,000	100,000,000
Common stock issued (shares)	55,341,000	45,272,000
Common stock outstanding (shares)	55,341,000	45,272,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Collaboration revenue	$ 1,249	$ 0
Operating expenses:
Research and development	33,240	24,352
Selling, general and administrative	21,318	10,918
Acquired in-process research and development expense	1,500	0
Change in fair value of contingent consideration	(7,900)	3,000
Total operating expenses	48,158	38,270
Loss from operations	(46,909)	(38,270)
Other income (expense):
Interest income	1,088	3,156
Other income (expense), net	20,021	(88)
Total other income	21,109	3,068
Net loss	$ (25,800)	$ (35,202)
Net loss per share, basic and diluted
Net loss per share, basic and diluted (in dollars per share)	$ (0.54)	$ (0.83)
Weighted average number of shares used in the calculation of basic and diluted net loss per common share (shares)	48,185	42,236

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net loss	$ (25,800)	$ (35,202)
Other comprehensive (loss) income, net of tax:
Change in unrealized (losses) gains related to marketable securities	(172)	370
Foreign currency translation adjustments	5	0
Total other comprehensive (loss) income	(167)	370
Comprehensive loss	$ (25,967)	$ (34,832)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Stockholders' Equity Beginning Balance at Dec. 31, 2018	$ 522,801	$ 42	$ 1,218,710	$ 3	$ (695,954)
Stockholders' Equity - Beginning Balance (shares) at Dec. 31, 2018		42,078
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(35,202)				(35,202)
Other comprehensive income (loss)	370			370
Issuance of common stock under employee equity plans	5,293		5,293
Issuance of common stock under employee equity plans (shares)		380
Shares repurchased for tax withholdings related to net share settlement of employee equity awards	(606)		(606)
Shares repurchased for tax withholdings related to net share settlement of employee equity awards (shares)		(12)
Stock-based compensation	4,223		4,223
Stockholders' Equity Ending Balance at Mar. 31, 2019	496,879	$ 42	1,227,620	373	(731,156)
Stockholders' Equity - Ending Balance (shares) at Mar. 31, 2019		42,446
Stockholders' Equity Beginning Balance at Dec. 31, 2019	245,059	$ 45	1,360,092	379	(1,115,457)
Stockholders' Equity - Beginning Balance (shares) at Dec. 31, 2019		45,272
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(25,800)				(25,800)
Other comprehensive income (loss)	(167)			(167)
Issuance of common stock, net of offering costs	221,708	$ 10	221,698
Issuance of common stock, net of offering costs (shares)		9,798
Issuance of common stock under employee equity plans	3,882		3,882
Issuance of common stock under employee equity plans (shares)		297
Shares repurchased for tax withholdings related to net share settlement of employee equity awards	(569)		(569)
Shares repurchased for tax withholdings related to net share settlement of employee equity awards (shares)		(26)
Stock-based compensation	6,394		6,394
Stockholders' Equity Ending Balance at Mar. 31, 2020	$ 450,507	$ 55	$ 1,591,497	$ 212	$ (1,141,257)
Stockholders' Equity - Ending Balance (shares) at Mar. 31, 2020		55,341

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flow from operating activities:
Net loss	$ (25,800)	$ (35,202)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	6,394	4,223
Depreciation and amortization	357	191
Noncash lease expense	339
Net accretion and amortization of investments in marketable securities	(215)	(1,703)
Change in fair value of warrant liabilities	(162)	303
Acquired in-process research and development expense	1,500	0
Change in fair value of contingent consideration	(7,900)	3,000
Changes in operating assets and liabilities:
Accounts receivable	0	(15,500)
Other receivable	(19,741)	0
Prepaid expenses, escrow holdback and other current assets	(722)	5,270
Other assets	(405)
Accounts payable, accrued and other liabilities	(4,435)	(7,096)
Operating lease liability	(452)
Deferred revenue	(1,249)	15,500
Net cash used in operating activities	(52,491)
Cash flows from investing activities:
Cash paid for in-process research and development asset	(1,500)	0
Purchases of marketable securities	(15,695)	(145,826)
Proceeds from maturities of marketable securities	54,605	171,225
Purchases of property and equipment	(193)	(4,535)
Net cash provided by investing activities	37,217	20,864
Cash flows from financing activities:
Payment of contingent consideration	0	(10,000)
Proceeds from issuance of common stock under equity incentive plans	2,040	4,379
Taxes paid related to net share settlement of equity awards	(569)	(582)
Proceeds from issuance of common stock, net of issuance costs	221,708	0
Net cash provided by (used in) financing activities	223,179	(6,203)
Net decrease in cash and cash equivalents	207,905	(10,166)
Cash and cash equivalents, beginning of the period	62,070	68,454
Cash and cash equivalents, end of the period	$ 269,975	$ 58,288

Organization, Basis of Presenta

Organization, Basis of Presentation and Liquidity	3 Months Ended
	Mar. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization, Basis of Presentation and Liquidity	Organization, Basis of Presentation and Liquidity Zogenix, Inc. and subsidiaries (the Company, we, us or our) is a global pharmaceutical company committed to developing and commercializing transformative therapies to improve the lives of patients and their families living with rare diseases. We are primarily focused on developing and commercializing two therapeutic product candidates: Fintepla, a low-dose fenfluramine investigational therapy for two pediatric epilepsy disorders, Dravet syndrome and Lennox-Gastaut Syndrome (LGS); and MT1621, an investigational deoxynucleoside substrate enhancement therapy for the treatment of thymidine kinase 2 deficiency (TK2d), an inherited mitochondrial DNA depletion disorder that predominantly affects children and is often fatal. We operate in one business segment—the research, development and commercialization of pharmaceutical products and our headquarters are located in Emeryville, California. Basis of Presentation The accompanying condensed consolidated financial statements include the accounts of Zogenix, Inc. and its wholly-owned subsidiaries. Intercompany accounts and transactions have been eliminated in consolidation. The condensed consolidated financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (SEC) for interim financial reporting. In the opinion of management, the condensed consolidated financial statements reflect all adjustments, which are normal and recurring in nature, necessary for fair financial statement presentation. The results of operations for any interim period are not necessarily indicative of results of operations for any future period. Certain information and footnote disclosures normally included in annual consolidated financial statements prepared in accordance with generally accepted accounting principles in the United States (GAAP) have been condensed or omitted. Accordingly, these unaudited interim condensed consolidated financial statements and accompanying notes should be read in conjunction with the consolidated financial statements and related notes included in our 2019 Annual Report on Form 10-K (2019 Form 10-K), which was filed with the SEC on March 2, 2020. Certain prior period amounts within the accompanying unaudited condensed consolidated financial statements have been reclassified to conform to current period presentation. These reclassifications did not affect our financial position, net loss, comprehensive loss, or cash flows as of and for the periods presented. Future Funding Requirements As of March 31, 2020, our cash, cash equivalents and marketable securities totaled $420.2 million. Excluding gains from two discrete business divestitures, we have incurred significant net losses and negative cash flows from operating activities since inception resulting in an accumulated deficit of $1.1 billion as of March 31, 2020. We expect to continue to incur significant operating losses and negative cash flows from operations as we continue to advance our product candidates through development and commercialization. Additionally, we are obligated to make future milestone payments that are contingent upon the successful achievement of certain regulatory and sales-based milestone events related to Fintepla and certain regulatory milestone events related to MT1621. Historically, we have relied primarily on the proceeds from equity offerings to finance our operations. Until such time, if ever, we can generate a sufficient amount of revenue to finance our cash requirements, we may need to continue to rely on additional financing to achieve our business objectives. However, if such financing is not available at adequate levels when needed, we may be required to significantly delay, scale back or discontinue one or more of our product development programs or commercialization efforts or other aspects of our business plans, and our operating results and financial condition would be adversely affected.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Use of Estimates The preparation of our condensed consolidated financial statements requires us to make estimates, judgments and assumptions that may affect the reported amounts of assets, liabilities, equity, revenues and expenses and related disclosure of contingent assets and liabilities. On an ongoing basis we evaluate our estimates, judgments and methodologies. We base our estimates on historical experience and on various other assumptions that we believe are reasonable, the results of which form the basis for making judgments about the carrying values of assets, liabilities and equity and the amount of revenues and expenses. Actual results may differ from those estimates. Significant Accounting Policies The significant accounting policies and estimates used in the preparation of the accompanying condensed consolidated financial statements are described in Note 2, Summary of Significant Accounting Policies of notes to the consolidated financial statements in our 2019 Form 10-K. There have been no material changes in our significant accounting policies during the three months ended March 31, 2020 other than the recently adopted accounting pronouncements set forth below. Impact of COVID-19 Pandemic In March 2020, the World Health Organization declared the global novel coronavirus disease (COVID-19) outbreak a pandemic. To date, our operations have not been significantly impacted by the COVID-19 outbreak. However, we cannot predict the specific extent, duration, or full impact that the COVID-19 outbreak will have on our financial condition and operations, including ongoing and planned clinical trials, the timelines for receiving feedback or approvals from regulatory authorities, and a potential product launch in the midst of a pandemic. Management is monitoring the potential impact of the COVID-19 pandemic, if any, on the carrying value of our indefinite-lived in-process research and development (IPR&D) intangible asset, goodwill, long-lived assets and right-of-use assets. The full extent to which the COVID-19 pandemic will directly or indirectly impact our business, results of operations and financial condition, will depend on future developments that are highly uncertain, including as a result of new information that may emerge concerning COVID-19 and the actions taken to contain it or treat COVID-19, as well as the economic impact on local, regional, national and international markets. If the financial markets and/or the overall economy are impacted for an extended period, our business, results of operations and financial condition may be adversely affected. Income Taxes On March 27, 2020, The Coronavirus Aid, Relief and Economic Security Act (CARES Act) was signed into law which lifts certain limitations originally imposed by the Tax Cuts and Jobs Act of 2017 (Tax Act). The CARES Act, among other provisions, retroactively and temporarily (for taxable years beginning before January 1, 2021) suspends application of the 80%-of-income limitation on the use of net operating losses, which was enacted as part of the Tax Act. It also provides that net operating losses arising in any taxable year beginning after December 31, 2017, and before January 1, 2021 are generally eligible to be carried back up to five years. The enactment of the CARES Act did not result in any material adjustments to our income tax provision for the three months ended March 31, 2020 or to our net deferred tax assets as of March 31, 2020. Given our history of losses, we do not expect the provisions of the CARES Act to have a material impact on our annual effective tax rate or condensed consolidated financial statements in 2020; however, we will continue to evaluate the impact of tax legislation and will update our disclosures as additional information and interpretive guidance becomes available. Recently Adopted Accounting Pronouncements Accounting Standards Update (ASU) 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments revises the measurement of credit losses for most financial instruments measured at amortized cost, including trade receivables, from an incurred loss methodology to an expected loss methodology which results in earlier recognition of credit losses. Under the incurred loss model, a loss is not recognized until it is probable that the loss-causing event has already occurred. The standard introduces a forward-looking expected credit loss model that requires an estimate of the expected credit losses over the life of the instrument by considering all relevant information including historical experience, current conditions, and reasonable and supportable forecasts that affect collectability. In addition, the standard also modifies the impairment model for available-for-sale debt securities, which are measured at fair value, by eliminating the consideration for the length of time fair value has been less than amortized cost when assessing credit loss for a debt security and provides for reversals of credit losses through income upon credit improvement. The standard became effective for us beginning January 1, 2020. Based on the composition of our investment portfolio, which reflects our primary investment objective of capital preservation, the adoption of this standard did not have a material impact on our condensed consolidated financial statements or related disclosures. ASU 2017-04, Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment simplifies how an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Step 2 measures a goodwill impairment loss by comparing the implied fair value of a reporting unit’s goodwill with the carrying amount of that goodwill. The implied fair value for a reporting unit is determined in the same manner as the amount of goodwill recognized in a business acquisition of the reporting unit. Under the standard, an entity shall recognize an impairment charge for the amount by which the carrying amount of a reporting unit exceeds its fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. The standard became effective for us beginning January 1, 2020. The adoption of this standard did not have a material impact on our condensed consolidated financial statements or related disclosures; however, any prospective goodwill impairment losses recognized will be measured in accordance with the updated guidance. ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework — Changes to the Disclosure Requirements for Fair Value Measurement modifies the disclosure requirements in Topic 820 by removing certain disclosure requirements related to the fair value hierarchy, modifying existing disclosure requirements related to measurement uncertainty and adding new disclosure requirements, such as disclosing the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. This standard became effective for us beginning January 1, 2020 and the adoption of this standard did not have a material impact on our condensed consolidated financial statements. For the new disclosures regarding our Level 3 fair value measurements, see Note 5, Fair Value Measurements to these condensed consolidated financial statements. ASU 2019-12, Simplifying the Accounting for Income Taxes (Topic 740 ) removes certain exceptions to the general principles in Topic 740 related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. The new guidance also simplifies aspects of the accounting for franchise taxes and enacted changes in tax laws or rates and clarifies the accounting for transactions that result in a step-up in the tax basis of goodwill. This ASU is effective for us for all interim and annual periods beginning January 1, 2021, with early adoption permitted. We early adopted ASU 2019-12 beginning January 1, 2020 on a prospective basis. The adoption of this standard did not have a material impact on our condensed consolidated financial statements and related disclosures. The only aspect of ASU 2019-12 that is currently applicable to us is the removal of the exception related to intraperiod tax allocation. Beginning in 2020, we will apply the general methodology regarding the intraperiod allocation of tax expense. After the adoption of ASU 2019-12, in periods where we have a loss from continuing operations, we will determine the amount of taxes attributable to continuing operations without regard to the tax effect of other items, including changes in unrealized gains related to marketable securities. Recent Accounting Pronouncements We have reviewed recently issued accounting pronouncements and concluded they are either not applicable to our business or no material effect is expected on our condensed consolidated financial statements as a result of future adoption.

Collaborative Arrangement

Collaborative Arrangement	3 Months Ended
	Mar. 31, 2020
Disaggregation of Revenue [Abstract]
Collaborative Arrangement	Collaborative Arrangement In March 2019, we entered into an agreement (Shinyaku Agreement) with Nippon Shinyaku Co., Ltd. (Shinyaku) for the exclusive distribution of Fintepla in Japan for the treatment of Dravet syndrome and LGS. As part of the Shinyaku Agreement, we are responsible for completing the global clinical development and all regulatory approval activities for Fintepla to support the submission of new drug applications in Japan for Dravet syndrome and LGS. Upon regulatory approval of Fintepla in Japan, Shinyaku will act as our exclusive distributor for Fintepla and will be responsible for the commercialization activities including the promotion, marketing, sale and distribution of Fintepla in Japan. Upon regulatory approval of Fintepla in Japan, Shinyaku will also act as our exclusive distributor for commercial shipment and distribution of Fintepla in Japan. If we pursue global development of Fintepla for indications other than Dravet syndrome or LGS, Shinyaku has the option to participate in the development for such indications in Japan, subject to cost sharing requirements pursuant to the agreement. Activities under the Shinyaku Agreement will be governed by a joint steering committee (JSC) consisting of three representatives from each party to the agreement. All decisions of the JSC are to be made by a unanimous vote with tie-breaking rights provided to each party for certain matters related to development, regulatory approval and commercialization select distribution activities of Fintepla in that territory. Shinyaku has agreed to support development and regulatory approval of Fintepla in Japan by actively participating in the design of non-clinical, clinical and manufacturing requirements needed for regulatory submission, actively planning and participating in product labeling decisions and discussions with the Japanese Ministry of Health, Labor and Welfare (MHLW) and obtained distribution exclusivity through the payment of an initial fixed consideration. Pursuant to the terms of the agreement, Shinyaku agreed to make aggregate fixed payments of $20.0 million to us in scheduled installments. As of March 31, 2020, we have received $17.0 million with the remaining balance due within the next year. We will be actively running the clinical trials, performing manufacturing validation activities, preparing regulatory filings and holding discussions with MHLW, and negotiating pricing. We and Shinyaku have agreed to proportionally share the Japan specific development costs that may arise outside of the initial development plan and any post-approval clinical study costs in Japan. In addition, we can earn up to $66.0 million from Shinyaku for the achievement of certain regulatory milestones for the treatment of Dravet syndrome and LGS. If regulatory approval of Fintepla is received in Japan, we have agreed to supply Shinyaku with Fintepla upon receipt of purchase orders at our actual manufacturing cost plus a fixed transfer price mark-up, a fixed percentage of Shinyaku's net sales of Fintepla in Japan for such fiscal year, and a net price mark-up based on a percent of the applicable aggregate sales of Fintepla by Shinyaku for such fiscal year. The net price mark-up percentage increases with Shinyaku’s sales of Fintepla annual net sales in Japan and ranges between mid-twenties and is capped at a low thirties of the aggregate annual net sales for an applicable fiscal year. In addition, we can earn up to an additional $42.5 million tied to the achievement of certain net sales milestones by Shinyaku through the term of the agreement, which generally expires in 2045. The collaborative activities under the Shinyaku Agreement prior to regulatory approval are within the scope of the accounting guidance related to collaborative arrangements as both parties are active participants and are exposed to significant risks and rewards dependent on the success of commercializing Fintepla in Japan. Since Shinyaku is not a customer as it does not obtain an output of our development and regulatory approval activities for Fintepla as they were not provided a license to our intellectual property or the ability to manufacture the product, and we do not consider performing development and regulatory approval services to be a part of our ongoing activities. Shinyaku will only become a customer and subject to revenue from contracts from customers accounting guidance after regulatory approval of Fintepla in Japan occurs and Shinyaku places purchase orders with us. To date, Shinyaku has not provided us with any purchase orders and thus no revenue has been recognized for the supply of Fintepla. We considered the revenue from contracts with customers guidance by analogy in determining the unit of account, and the recognition and measurement of such unit of account for collaborative activities under the Shinyaku Agreement and concluded that there are two development programs akin to performance obligations related to collaborative activities for development and regulatory approval efforts for Dravet and LGS. We are the principal as it relates to the collaborative development and regulatory approval activities primarily because we are responsible for the acceptability of the results of the work of the third-party vendors that are used to assist us in performing such activities. Therefore, such collaboration revenue is presented on a gross basis in our condensed consolidated statements of operations apart from research and development expenses incurred . Since Shinyaku was not provided a license to our intellectual property or the ability to manufacture Fintepla, Shinyaku will only become a customer, and payments made under the Shinyaku Agreement will only be subject to the accounting guidance related to revenue from contracts from customers, after regulatory approval of Fintepla in Japan occurs and Shinyaku places purchase orders with us. The initial collaboration consideration consisted solely of the fixed consideration payments of $20.0 million and was allocated on a relative standalone selling price basis to the two identified development programs akin to performance obligations related to collaborative activities for development and regulatory approval efforts for Dravet syndrome and LGS. Analogizing to the revenue from contracts with customers variable consideration guidance, all potential regulatory milestone payment consideration will be included in the collaboration consideration if and when it is probable that a significant reversal in the amount of cumulative collaboration consideration recognized will not occur when the uncertainty associated with the variable collaboration consideration is subsequently resolved. At contract inception and through March 31, 2020, this consideration was fully constrained as the achievement of the events tied to these regulatory milestone payments was highly dependent on factors outside our control. Collaboration revenue is being recognized over time as the collaborative activities related to each development program are rendered. We determined an input method is a reasonable representative depiction of the performance of the collaborative activities under the Shinyaku Agreement. The method of measuring progress towards completion incorporates actual internal and external costs incurred, relative to total internal and external costs expected to be incurred over an estimated period to satisfy the collaborative activities. The period over which total costs are estimated reflects our estimate of the period over which it will perform the collaborative activities for each development program. Changes in estimates of total internal and external costs expected to be incurred are recognized in the period of change as a cumulative catch-up adjustment to collaboration revenue.

Cash, Cash Equivalents and Mark

Cash, Cash Equivalents and Marketable Securities	3 Months Ended
	Mar. 31, 2020
Cash and Cash Equivalents [Abstract]
Cash, Cash Equivalents, and Marketable Securities	Cash, Cash Equivalents and Marketable Securities The following tables summarize the amortized cost and the estimated fair value of our cash, cash equivalents and marketable securities as of March 31, 2020 and December 31, 2019 (in thousands): March 31, 2020 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Current assets: Cash $ 11,271 $ — $ — $ 11,271 Cash equivalents: Money market funds 224,070 — — 224,070 Commercial paper 34,634 — — 34,634 Total cash and cash equivalents 269,975 — — 269,975 Marketable securities: Commercial paper 39,528 — — 39,528 Corporate debt securities 70,543 273 (66) 70,750 Certificate of deposits 39,940 — — 39,940 Total marketable securities 150,011 273 (66) 150,218 Total cash, cash equivalents and marketable securities $ 419,986 $ 273 $ (66) $ 420,193 December 31, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Current assets: Cash $ 43,058 $ — $ — $ 43,058 Cash equivalents: Money market funds 11,527 — — 11,527 Commercial paper 7,485 — — 7,485 Total cash and cash equivalents 62,070 — — 62,070 Marketable securities: Commercial paper 73,366 — — 73,366 Corporate debt securities 74,038 381 (2) 74,417 Certificate of deposits 41,302 — — 41,302 Total marketable securities 188,706 381 (2) 189,085 Total cash, cash equivalents and marketable securities $ 250,776 $ 381 $ (2) $ 251,155 The following table summarizes the cost and fair value of marketable securities based on stated effective maturities as of March 31, 2020 (in thousands): Amortized Cost Fair Value Due within one year $ 127,968 $ 128,147 Due between one and two years 22,043 22,071 Total $ 150,011 $ 150,218 We regularly review our available-for-sale marketable securities in an unrealized loss position and evaluate the current expected credit loss by considering factors such as historical experience, market data, issuer-specific factors, and current economic conditions. For all marketable securities that have been in a continuous loss position as of March 31, 2020, we have the ability and intent to hold until maturity or recovery. We determined the gross unrealized losses were caused by market fluctuations. There have been no specific facts or circumstances that have arisen to indicate that there has been any significant deterioration in the creditworthiness of the issuers of these securities. As such, we determined no allowance for credit losses was deemed necessary. Accrued interest receivable is recorded in “Prepaid expenses and other current assets” on our condensed consolidated balance sheets and was $0.7 million and $0.6 million as of March 31, 2020 and December 31, 2019, respectively. See Note 5 for further information regarding the fair value of our financial instruments.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. A three-level valuation hierarchy has been established under GAAP for disclosure of fair value measurements. The valuation hierarchy is based on the transparency of inputs to the valuation of an asset or liability as of the measurement date. The three levels are defined as follows: Level 1: Observable inputs such as quoted prices in active markets; Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly; and Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions. Our financial instruments consist primarily of cash and cash equivalents, marketable securities, other current assets, accounts payable and accrued liabilities, contingent consideration liabilities and our outstanding common stock warrant liabilities. Certain cash equivalents, marketable securities, contingent consideration liabilities and common stock warrant liabilities are reported at their respective fair values on our condensed consolidated balance sheets. The remaining financial instruments are carried at cost which approximates their respective fair values because of the short-term nature of these financial instruments. See Note 4 for further information regarding the amortized cost of our financial assets. The following tables summarize assets and liabilities recognized or disclosed at fair value on a recurring basis as of March 31, 2020 and December 31, 2019 (in thousands): March 31, 2020 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Commercial paper $ — $ 34,634 $ — $ 34,634 Money market funds 224,070 — 224,070 Marketable securities: Commercial paper — 39,528 — 39,528 Corporate debt securities — 70,750 — 70,750 Certificate of deposits — 39,940 — 39,940 Total assets (1) $ 224,070 $ 184,852 $ — $ 408,922 Liabilities: Common stock warrant liabilities $ — $ — $ 36 $ 36 Contingent consideration liabilities — — 55,900 55,900 Total liabilities $ — $ — $ 55,936 $ 55,936 December 31, 2019 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 11,527 $ — $ — $ 11,527 Commercial paper — 7,485 — $ 7,485 Marketable securities: Commercial paper — 73,366 — 73,366 Corporate debt securities — 74,417 — 74,417 Certificate of deposits — 41,302 — 41,302 Total assets (1) $ 11,527 $ 196,570 $ — $ 208,097 Liabilities: Common stock warrant liabilities $ — $ — $ 198 $ 198 Contingent consideration liabilities — — 63,800 63,800 Total liabilities $ — $ — $ 63,998 $ 63,998 (1) Fair value is determined by taking into consideration valuations obtained from third-party pricing services. The third-party pricing services utilize industry standard valuation models, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker/dealer quotes on the same or similar securities; issuer credit spreads; benchmark securities; and other observable inputs. Contingent Consideration Liability Pursuant to the terms of the Brabant purchase agreement in 2014 in which we acquired worldwide development and commercialization rights to Fintepla, we are obligated to make future milestone payments that are contingent upon the successful achievement of certain regulatory and sales-based milestone events related to Fintepla. The potential amount of future payments that we may be required to make is between zero, if none of the remaining milestones are achieved, to a maximum of $75.0 million. The following table provides a reconciliation of our contingent consideration liability measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the three months ended March 31, 2020 and 2019 (in thousands): Three Months Ended March 31, 2020 2019 Balance at beginning of period $ 63,800 $ 78,200 Change in fair value (7,900) 3,000 Settlements — (10,000) Balance at end of period $ 55,900 $ 71,200 The decrease in fair value of our contingent consideration for the three months ended March 31, 2020 was primarily due to changes to our probability-weighted estimates for achieving regulatory/commercial milestones and the use of a higher discount rate to reflect an increase in credit-adjusted interest rates. The increase in fair value of our contingent consideration for the three months ended March 31, 2019 was primarily due to the inclusion of sales in Japan in our forecast associated with the execution of the Shinyaku Agreement, which accelerated the estimated timing of when certain sales milestones will be reached, and a market driven decrease in the discount rate. The following table summarizes the significant unobservable inputs used in the fair value measurement of our contingent consideration liabilities as of March 31, 2020. Fair Value Valuation Technique Unobservable Input Range Weighted $55,900 Discounted cash flow Discount rate 6.5% — 14.8% 9.8% Probability of payment 0% — 85.1% 85.1% Projected year of payment 2020 — 2030 2022 (1) Unobservable inputs were weighted by the relative fair value of the contingent consideration liability. For projected year of payment, the amount represents the median of the inputs and is not a weighted average. The weighted average discount rate was calculated based on the relative fair value of our contingent consideration obligations. Significant increases or decreases in projected revenues, probabilities of payment, discount rates or the time until payment is made would have resulted in a significantly lower or higher fair value measurement as of March 31, 2020.

Accrued and Other Current Liabi

Accrued and Other Current Liabilities	3 Months Ended
	Mar. 31, 2020
Payables and Accruals [Abstract]
Accrued and Other Current Liabilities	Accrued and Other Current Liabilities The following table provides details of accrued and other current liabilities (in thousands): March 31, 2020 December 31, 2019 Accrued clinical trial expenses $ 14,215 $ 18,666 Accrued compensation 4,930 7,179 Other accrued liabilities 6,622 4,074 Common stock warrant liabilities 36 198 Total accrued and other current liabilities $ 25,803 $ 30,117

Leases

Leases	3 Months Ended
	Mar. 31, 2020
Leases [Abstract]
Leases	Leases We have operating leases consisting of office space for our Emeryville, California headquarters and for our various subsidiaries. In March 2020, our operating lease for our former headquarters in San Diego, California and the co-terminus sublease arrangement with our sublessee expired in accordance with the terms of the leases. In February 2020, we entered into a lease for office space in Maidenhead, United Kingdom, for a five The components of lease costs, which were included in our condensed consolidated statements of operations, were as follows (in thousands): Three Months Ended March 31, 2020 2019 Lease costs Operating lease cost $ 567 $ 499 Short-term lease cost (1) 157 328 Sublease income (115) (145) Total $ 609 $ 682 (1) Short-term lease cost included $0.2 million related to a short-term lease that expired in March 2019. Cash paid for amounts included in the measurement of lease liabilities for the three months ended March 31, 2020 and 2019 was $0.6 million and $0.3 million, respectively. The amounts were included in net cash used in operating activities in our condensed consolidated statements of cash flows. Right-of-use assets obtained in exchange for new operating lease liabilities were $1.2 million for the three months ended March 31, 2020. Maturities of operating lease liabilities as of March 31, 2020 and December 31, 2019 were as follows (in thousands): March 31, 2020 December 31, 2019 2020 (remaining 9 months and 12 months, respectively) $ 1,533 $ 1,986 2021 2,292 1,957 2022 2,230 1,894 2023 2,287 1,951 2024 2,300 2,010 Thereafter 5,103 5,101 Total lease payments 15,745 14,899 Less imputed interest (2,908) (2,825) Total operating lease liabilities $ 12,837 $ 12,074 March 31, 2020 December 31, 2019 Current portion of operating lease liabilities $ 1,383 $ 1,322 Operating lease liabilities, net of current portion 11,454 10,752 Total lease liabilities $ 12,837 $ 12,074 As of March 31, 2020, the weighted average remaining lease term was 6.8 years and the weighted average discount rate, weighted based on the remaining balance of lease payments, was 6.2%.

Stockholders' Equity and Stock-

Stockholders' Equity and Stock-Based Compensation	3 Months Ended
	Mar. 31, 2020
Share-based Payment Arrangement [Abstract]
Stockholders' Equity and Stock-Based Compensation	Stockholders’ Equity and Stock-Based Compensation Sale of Common Stock In March 2020, we completed an underwritten public offering of 9,798,000 shares of our common stock at an offering price of $23.50 per share, including 1,278,000 shares sold pursuant to the underwriters’ full exercise of their option to purchase additional shares. Net proceeds realized from the offering amounted to approximately $221.7 million, after deducting commissions and other offering expenses. Equity Incentive Plans We have issued stock-based awards from various equity incentive and stock purchase plans, as more fully described in Note 12, Stock-Based Compensation to the consolidated financial statements in our 2019 Form 10-K. Stock Options The following is a summary of stock option activity for the three months ended March 31, 2020 (in thousands, except per share data): Shares Weighted- Average Exercise Price per Share Outstanding at December 31, 2019 4,253 $ 29.59 Granted 841 30.11 Exercised (230) 16.87 Canceled (65) 37.07 Outstanding at March 31, 2020 4,799 $ 30.19 Restricted Stock Units The following is a summary of restricted stock unit activity for the three months ended March 31, 2020 (in thousands, except per share data): Shares Weighted- Average Fair Value per Share at Grant Date Outstanding at December 31, 2019 439 $ 36.97 Granted 216 27.36 Vested (66) 48.41 Canceled (8) 37.56 Outstanding at March 31, 2020 581 $ 32.11 Stock-Based Compensation Expense Allocation The following table summarizes the components of total stock-based compensation expense included in the condensed consolidated statements of operations (in thousands): Three Months Ended March 31, 2020 2019 Research and development $ 2,729 $ 1,435 Selling, general and administrative 3,665 2,788 Total $ 6,394 $ 4,223

Net Loss Per Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2020
Earnings Per Share [Abstract]
Net Loss per Share	Net Loss Per Share Basic net loss per share is calculated by dividing net loss by the weighted average number of shares outstanding for the period. Diluted net loss per share is calculated by dividing net loss by the weighted average number of shares of common stock and potential dilutive common stock equivalents outstanding during the period if the effect is dilutive. Our potentially dilutive shares of common stock include outstanding stock options, restricted stock units and warrants to purchase common stock. A reconciliation of the numerators and denominators used in computing net loss per share is as follows (in thousands, except per share amounts): Three Months Ended March 31, 2020 2019 Numerator: Net loss $ (25,800) $ (35,202) Denominator: Shares used in per share calculation 48,185 42,236 Net loss per share, basic and diluted $ (0.54) $ (0.83) The following table presents the potential shares of common stock outstanding that were excluded from the calculation of diluted net loss per share for the periods presented because including them would have been anti-dilutive (in thousands): Three Months Ended March 31, 2020 2019 Shares subject to outstanding stock options 4,450 3,716 Shares subject to outstanding restricted stock units 485 295 Shares subject to outstanding warrants to purchase common stock 28 28 Total 4,963 4,039

United Kingdom (U.K.) Research

United Kingdom (U.K.) Research and Development Incentives	3 Months Ended
	Mar. 31, 2020
Other Income and Expenses [Abstract]
United Kingdom (U.K.) Research and Development Incentives	United Kingdom (U.K.) Research and Development (R&D) Tax Relief Scheme We conduct extensive research and development activities that benefit from U.K.’s small and medium-sized enterprises (SMEs) R&D tax relief scheme. Under this tax relief scheme, a SME has an option to receive an enhanced U.K. tax deduction on its eligible R&D activities or, when an SME entity is in a net operating loss position, can elect to surrender net operating losses that arise from its eligible R&D activities in exchange for a cash payment from the U.K. tax authorities. As the tax incentives may be received without regard to an entity’s actual tax liability, they are not subject to accounting for income taxes. Amounts recognized by us for cash payment claims under the SME R&D tax relief scheme are recorded as a component of other income after an election for tax relief has been made by submitting a claim for a discrete tax year and collectability is deemed probable and reasonably assured. As of December 31, 2019, we submitted claims as an SME for a total amount of $19.7 million, consisting of tax credit cash rebates of $9.9 million and $9.8 million for our 2017 and 2018 tax years, respectively. In April 2020, we received correspondence from the U.K. tax authorities informing us the claim has been approved. As a result, the amount of the claim was recorded as other receivable on the condensed consolidated balance sheet at March 31, 2020 and recognized as a component of other income on the condensed consolidated statement of operations for the three months ended March 31, 2020. For our 2019 tax year, we have not yet decided whether to seek tax relief by surrendering some of our losses for a tax credit cash rebate claim or electing to receive enhanced U.K. tax deductions on our eligible research and development activities. Under the U.K’s tax legislation, there is a two

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2020
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of our condensed consolidated financial statements requires us to make estimates, judgments and assumptions that may affect the reported amounts of assets, liabilities, equity, revenues and expenses and related disclosure of contingent assets and liabilities. On an ongoing basis we evaluate our estimates, judgments and methodologies. We base our estimates on historical experience and on various other assumptions that we believe are reasonable, the results of which form the basis for making judgments about the carrying values of assets, liabilities and equity and the amount of revenues and expenses. Actual results may differ from those estimates.
Impact of COVID-19 Pandemic	Impact of COVID-19 Pandemic In March 2020, the World Health Organization declared the global novel coronavirus disease (COVID-19) outbreak a pandemic. To date, our operations have not been significantly impacted by the COVID-19 outbreak. However, we cannot predict the specific extent, duration, or full impact that the COVID-19 outbreak will have on our financial condition and operations, including ongoing and planned clinical trials, the timelines for receiving feedback or approvals from regulatory authorities, and a potential product launch in the midst of a pandemic. Management is monitoring the potential impact of the COVID-19 pandemic, if any, on the carrying value of our indefinite-lived in-process research and development (IPR&D) intangible asset, goodwill, long-lived assets and right-of-use assets. The full extent to which the COVID-19 pandemic will directly or indirectly impact our business, results of operations and financial condition, will depend on future developments that are highly uncertain, including as a result of new information that may emerge concerning COVID-19 and the actions taken to contain it or treat COVID-19, as well as the economic impact on local, regional, national and international markets. If the financial markets and/or the overall economy are impacted for an extended period, our business, results of operations and financial condition may be adversely affected.
Income Taxes	Income Taxes On March 27, 2020, The Coronavirus Aid, Relief and Economic Security Act (CARES Act) was signed into law which lifts certain limitations originally imposed by the Tax Cuts and Jobs Act of 2017 (Tax Act). The CARES Act, among other provisions, retroactively and temporarily (for taxable years beginning before January 1, 2021) suspends application of the 80%-of-income limitation on the use of net operating losses, which was enacted as part of the Tax Act. It also provides that net operating losses arising in any taxable year beginning after December 31, 2017, and before January 1, 2021 are generally eligible to be carried back up to five years. The enactment of the CARES Act did not result in any material adjustments to our income tax provision for the three months ended March 31, 2020 or to our net deferred tax assets as of March 31, 2020. Given our history of losses, we do not expect the provisions of the CARES Act to have a material impact on our annual effective tax rate or condensed consolidated financial statements in 2020; however, we will continue to evaluate the impact of tax legislation and will update our disclosures as additional information and interpretive guidance becomes available.
Recently Adopted Accounting Pronouncements and Recent Accounting Pronouncements	Recently Adopted Accounting Pronouncements Accounting Standards Update (ASU) 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments revises the measurement of credit losses for most financial instruments measured at amortized cost, including trade receivables, from an incurred loss methodology to an expected loss methodology which results in earlier recognition of credit losses. Under the incurred loss model, a loss is not recognized until it is probable that the loss-causing event has already occurred. The standard introduces a forward-looking expected credit loss model that requires an estimate of the expected credit losses over the life of the instrument by considering all relevant information including historical experience, current conditions, and reasonable and supportable forecasts that affect collectability. In addition, the standard also modifies the impairment model for available-for-sale debt securities, which are measured at fair value, by eliminating the consideration for the length of time fair value has been less than amortized cost when assessing credit loss for a debt security and provides for reversals of credit losses through income upon credit improvement. The standard became effective for us beginning January 1, 2020. Based on the composition of our investment portfolio, which reflects our primary investment objective of capital preservation, the adoption of this standard did not have a material impact on our condensed consolidated financial statements or related disclosures. ASU 2017-04, Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment simplifies how an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Step 2 measures a goodwill impairment loss by comparing the implied fair value of a reporting unit’s goodwill with the carrying amount of that goodwill. The implied fair value for a reporting unit is determined in the same manner as the amount of goodwill recognized in a business acquisition of the reporting unit. Under the standard, an entity shall recognize an impairment charge for the amount by which the carrying amount of a reporting unit exceeds its fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. The standard became effective for us beginning January 1, 2020. The adoption of this standard did not have a material impact on our condensed consolidated financial statements or related disclosures; however, any prospective goodwill impairment losses recognized will be measured in accordance with the updated guidance. ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework — Changes to the Disclosure Requirements for Fair Value Measurement modifies the disclosure requirements in Topic 820 by removing certain disclosure requirements related to the fair value hierarchy, modifying existing disclosure requirements related to measurement uncertainty and adding new disclosure requirements, such as disclosing the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. This standard became effective for us beginning January 1, 2020 and the adoption of this standard did not have a material impact on our condensed consolidated financial statements. For the new disclosures regarding our Level 3 fair value measurements, see Note 5, Fair Value Measurements to these condensed consolidated financial statements. ASU 2019-12, Simplifying the Accounting for Income Taxes (Topic 740 ) removes certain exceptions to the general principles in Topic 740 related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. The new guidance also simplifies aspects of the accounting for franchise taxes and enacted changes in tax laws or rates and clarifies the accounting for transactions that result in a step-up in the tax basis of goodwill. This ASU is effective for us for all interim and annual periods beginning January 1, 2021, with early adoption permitted. We early adopted ASU 2019-12 beginning January 1, 2020 on a prospective basis. The adoption of this standard did not have a material impact on our condensed consolidated financial statements and related disclosures. The only aspect of ASU 2019-12 that is currently applicable to us is the removal of the exception related to intraperiod tax allocation. Beginning in 2020, we will apply the general methodology regarding the intraperiod allocation of tax expense. After the adoption of ASU 2019-12, in periods where we have a loss from continuing operations, we will determine the amount of taxes attributable to continuing operations without regard to the tax effect of other items, including changes in unrealized gains related to marketable securities. Recent Accounting Pronouncements We have reviewed recently issued accounting pronouncements and concluded they are either not applicable to our business or no material effect is expected on our condensed consolidated financial statements as a result of future adoption.
Fair Value Measurements	Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. A three-level valuation hierarchy has been established under GAAP for disclosure of fair value measurements. The valuation hierarchy is based on the transparency of inputs to the valuation of an asset or liability as of the measurement date. The three levels are defined as follows: Level 1: Observable inputs such as quoted prices in active markets; Level 2: Inputs, other than the quoted prices in active markets, that are observable either directly or indirectly; and Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions.
Stock-based Compensation	We have issued stock-based awards from various equity incentive and stock purchase plans, as more fully described in Note 12, Stock-Based Compensation to the consolidated financial statements in our 2019 Form 10-K.
Net Loss per Share	Basic net loss per share is calculated by dividing net loss by the weighted average number of shares outstanding for the period. Diluted net loss per share is calculated by dividing net loss by the weighted average number of shares of common stock and potential dilutive common stock equivalents outstanding during the period if the effect is dilutive. Our potentially dilutive shares of common stock include outstanding stock options, restricted stock units and warrants to purchase common stock.

Cash, Cash Equivalents and Ma_2

Cash, Cash Equivalents and Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2020
Cash and Cash Equivalents [Abstract]
Amortized Cost and Fair Value of Cash, Cash Equivalents and Marketable Securities	The following tables summarize the amortized cost and the estimated fair value of our cash, cash equivalents and marketable securities as of March 31, 2020 and December 31, 2019 (in thousands): March 31, 2020 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Current assets: Cash $ 11,271 $ — $ — $ 11,271 Cash equivalents: Money market funds 224,070 — — 224,070 Commercial paper 34,634 — — 34,634 Total cash and cash equivalents 269,975 — — 269,975 Marketable securities: Commercial paper 39,528 — — 39,528 Corporate debt securities 70,543 273 (66) 70,750 Certificate of deposits 39,940 — — 39,940 Total marketable securities 150,011 273 (66) 150,218 Total cash, cash equivalents and marketable securities $ 419,986 $ 273 $ (66) $ 420,193 December 31, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Current assets: Cash $ 43,058 $ — $ — $ 43,058 Cash equivalents: Money market funds 11,527 — — 11,527 Commercial paper 7,485 — — 7,485 Total cash and cash equivalents 62,070 — — 62,070 Marketable securities: Commercial paper 73,366 — — 73,366 Corporate debt securities 74,038 381 (2) 74,417 Certificate of deposits 41,302 — — 41,302 Total marketable securities 188,706 381 (2) 189,085 Total cash, cash equivalents and marketable securities $ 250,776 $ 381 $ (2) $ 251,155
Cost and Fair Value of Marketable Securities	The following table summarizes the cost and fair value of marketable securities based on stated effective maturities as of March 31, 2020 (in thousands): Amortized Cost Fair Value Due within one year $ 127,968 $ 128,147 Due between one and two years 22,043 22,071 Total $ 150,011 $ 150,218

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2020
Fair Value Disclosures [Abstract]
Assets Measured at Fair Value on Recurring Basis	The following tables summarize assets and liabilities recognized or disclosed at fair value on a recurring basis as of March 31, 2020 and December 31, 2019 (in thousands): March 31, 2020 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Commercial paper $ — $ 34,634 $ — $ 34,634 Money market funds 224,070 — 224,070 Marketable securities: Commercial paper — 39,528 — 39,528 Corporate debt securities — 70,750 — 70,750 Certificate of deposits — 39,940 — 39,940 Total assets (1) $ 224,070 $ 184,852 $ — $ 408,922 Liabilities: Common stock warrant liabilities $ — $ — $ 36 $ 36 Contingent consideration liabilities — — 55,900 55,900 Total liabilities $ — $ — $ 55,936 $ 55,936 December 31, 2019 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 11,527 $ — $ — $ 11,527 Commercial paper — 7,485 — $ 7,485 Marketable securities: Commercial paper — 73,366 — 73,366 Corporate debt securities — 74,417 — 74,417 Certificate of deposits — 41,302 — 41,302 Total assets (1) $ 11,527 $ 196,570 $ — $ 208,097 Liabilities: Common stock warrant liabilities $ — $ — $ 198 $ 198 Contingent consideration liabilities — — 63,800 63,800 Total liabilities $ — $ — $ 63,998 $ 63,998
Liabilities Measured at Fair Value on Recurring Basis	The following tables summarize assets and liabilities recognized or disclosed at fair value on a recurring basis as of March 31, 2020 and December 31, 2019 (in thousands): March 31, 2020 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Commercial paper $ — $ 34,634 $ — $ 34,634 Money market funds 224,070 — 224,070 Marketable securities: Commercial paper — 39,528 — 39,528 Corporate debt securities — 70,750 — 70,750 Certificate of deposits — 39,940 — 39,940 Total assets (1) $ 224,070 $ 184,852 $ — $ 408,922 Liabilities: Common stock warrant liabilities $ — $ — $ 36 $ 36 Contingent consideration liabilities — — 55,900 55,900 Total liabilities $ — $ — $ 55,936 $ 55,936 December 31, 2019 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 11,527 $ — $ — $ 11,527 Commercial paper — 7,485 — $ 7,485 Marketable securities: Commercial paper — 73,366 — 73,366 Corporate debt securities — 74,417 — 74,417 Certificate of deposits — 41,302 — 41,302 Total assets (1) $ 11,527 $ 196,570 $ — $ 208,097 Liabilities: Common stock warrant liabilities $ — $ — $ 198 $ 198 Contingent consideration liabilities — — 63,800 63,800 Total liabilities $ — $ — $ 63,998 $ 63,998
Reconciliation of Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Level 3)	The following table provides a reconciliation of our contingent consideration liability measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the three months ended March 31, 2020 and 2019 (in thousands): Three Months Ended March 31, 2020 2019 Balance at beginning of period $ 63,800 $ 78,200 Change in fair value (7,900) 3,000 Settlements — (10,000) Balance at end of period $ 55,900 $ 71,200
Significant Inputs Used in Fair Value Measurement	The following table summarizes the significant unobservable inputs used in the fair value measurement of our contingent consideration liabilities as of March 31, 2020. Fair Value Valuation Technique Unobservable Input Range Weighted $55,900 Discounted cash flow Discount rate 6.5% — 14.8% 9.8% Probability of payment 0% — 85.1% 85.1% Projected year of payment 2020 — 2030 2022 (1) Unobservable inputs were weighted by the relative fair value of the contingent consideration liability. For projected year of payment, the amount represents the median of the inputs and is not a weighted average.

Accrued and Other Current Lia_2

Accrued and Other Current Liabilities (Tables)	3 Months Ended
	Mar. 31, 2020
Payables and Accruals [Abstract]
Details of Accrued and Other Current Liabilities	The following table provides details of accrued and other current liabilities (in thousands): March 31, 2020 December 31, 2019 Accrued clinical trial expenses $ 14,215 $ 18,666 Accrued compensation 4,930 7,179 Other accrued liabilities 6,622 4,074 Common stock warrant liabilities 36 198 Total accrued and other current liabilities $ 25,803 $ 30,117

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2020
Leases [Abstract]
Components of Lease Costs	The components of lease costs, which were included in our condensed consolidated statements of operations, were as follows (in thousands): Three Months Ended March 31, 2020 2019 Lease costs Operating lease cost $ 567 $ 499 Short-term lease cost (1) 157 328 Sublease income (115) (145) Total $ 609 $ 682 (1) Short-term lease cost included $0.2 million related to a short-term lease that expired in March 2019.
Maturities of Operating Lease Liabilities	Maturities of operating lease liabilities as of March 31, 2020 and December 31, 2019 were as follows (in thousands): March 31, 2020 December 31, 2019 2020 (remaining 9 months and 12 months, respectively) $ 1,533 $ 1,986 2021 2,292 1,957 2022 2,230 1,894 2023 2,287 1,951 2024 2,300 2,010 Thereafter 5,103 5,101 Total lease payments 15,745 14,899 Less imputed interest (2,908) (2,825) Total operating lease liabilities $ 12,837 $ 12,074 March 31, 2020 December 31, 2019 Current portion of operating lease liabilities $ 1,383 $ 1,322 Operating lease liabilities, net of current portion 11,454 10,752 Total lease liabilities $ 12,837 $ 12,074

Stockholders' Equity and Stoc_2

Stockholders' Equity and Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2020
Share-based Payment Arrangement [Abstract]
Summary of Stock Option Activity	The following is a summary of stock option activity for the three months ended March 31, 2020 (in thousands, except per share data): Shares Weighted- Average Exercise Price per Share Outstanding at December 31, 2019 4,253 $ 29.59 Granted 841 30.11 Exercised (230) 16.87 Canceled (65) 37.07 Outstanding at March 31, 2020 4,799 $ 30.19
Schedule of Restricted Stock Unit Activity	The following is a summary of restricted stock unit activity for the three months ended March 31, 2020 (in thousands, except per share data): Shares Weighted- Average Fair Value per Share at Grant Date Outstanding at December 31, 2019 439 $ 36.97 Granted 216 27.36 Vested (66) 48.41 Canceled (8) 37.56 Outstanding at March 31, 2020 581 $ 32.11
Stock-Based Compensation Expense	The following table summarizes the components of total stock-based compensation expense included in the condensed consolidated statements of operations (in thousands): Three Months Ended March 31, 2020 2019 Research and development $ 2,729 $ 1,435 Selling, general and administrative 3,665 2,788 Total $ 6,394 $ 4,223

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2020
Earnings Per Share [Abstract]
Basic and Diluted Net Loss Per Share	A reconciliation of the numerators and denominators used in computing net loss per share is as follows (in thousands, except per share amounts): Three Months Ended March 31, 2020 2019 Numerator: Net loss $ (25,800) $ (35,202) Denominator: Shares used in per share calculation 48,185 42,236 Net loss per share, basic and diluted $ (0.54) $ (0.83)
Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss per Share	The following table presents the potential shares of common stock outstanding that were excluded from the calculation of diluted net loss per share for the periods presented because including them would have been anti-dilutive (in thousands): Three Months Ended March 31, 2020 2019 Shares subject to outstanding stock options 4,450 3,716 Shares subject to outstanding restricted stock units 485 295 Shares subject to outstanding warrants to purchase common stock 28 28 Total 4,963 4,039

Organization, Basis of Presen_2

Organization, Basis of Presentation and Liquidity - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020USD ($)segment	Dec. 31, 2019USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments | segment	1
Total cash, cash equivalents and short-term investments, estimated fair value	$ 420,193	$ 251,155
Accumulated deficit	$ 1,141,257	$ 1,115,457

Collaborative Arrangement (Deta

Collaborative Arrangement (Details) - USD ($) $ in Thousands	3 Months Ended		13 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Collaboration revenue	$ 1,249	$ 0
Contract liability	12,100		$ 12,100
Fixed Consideration
Disaggregation of Revenue [Line Items]
Performance obligation at inception of arrangement	$ 20,000	20,000	20,000
Portion of fixed consideration received			$ 17,000
Variable Consideration | Achievement of Regulatory Milestones
Disaggregation of Revenue [Line Items]
Amount that can be earned upon achievement of milestone		66,000
Variable Consideration | Achievement of Net Sales Milestones
Disaggregation of Revenue [Line Items]
Amount that can be earned upon achievement of net sales milestone		$ 42,500

Cash, Cash Equivalents and Ma_3

Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Cash and Cash Equivalents [Line Items]
Cash	$ 11,271	$ 43,058
Total cash and cash equivalents	269,975	62,070
Marketable securities, amortized cost	150,011	188,706
Marketable securities, gross unrealized gains	273	381
Marketable securities, gross unrealized losses	(66)	(2)
Marketable securities, estimated fair value	150,218	189,085
Total cash, cash equivalents and marketable securities, amortized cost	419,986	250,776
Total cash, cash equivalents and marketable securities	420,193	251,155
Amortized Cost
Due within one year, amortized cost	127,968
Due between one and two years, amortized cost	22,043
Marketable securities, amortized cost	150,011
Fair Value
Due within one year, estimated fair value	128,147
Due between one and two years, estimated fair value	22,071
Marketable securities, estimated fair value	150,218
Prepaid expenses and other current assets
Fair Value
Accrued interest receivable	700	600
Commercial paper
Cash and Cash Equivalents [Line Items]
Cash equivalents	34,634	7,485
Marketable securities, amortized cost	39,528	73,366
Marketable securities, gross unrealized gains	0	0
Marketable securities, gross unrealized losses	0	0
Marketable securities, estimated fair value	39,528	73,366
Money market funds
Cash and Cash Equivalents [Line Items]
Cash equivalents	224,070	11,527
Corporate debt securities
Cash and Cash Equivalents [Line Items]
Marketable securities, amortized cost	70,543	74,038
Marketable securities, gross unrealized gains	273	381
Marketable securities, gross unrealized losses	(66)	(2)
Marketable securities, estimated fair value	70,750	74,417
Certificate of deposits
Cash and Cash Equivalents [Line Items]
Marketable securities, amortized cost	39,940	41,302
Marketable securities, gross unrealized gains	0	0
Marketable securities, gross unrealized losses	0	0
Marketable securities, estimated fair value	$ 39,940	$ 41,302

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term fixed income securities	$ 150,218,000	$ 189,085,000
Total assets	408,922,000	208,097,000
Common stock warrant liabilities	36,000	198,000
Total liabilities	55,936,000	63,998,000
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	224,070,000	11,527,000
Total liabilities	0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	184,852,000	196,570,000
Total liabilities	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Contingent consideration liabilities	55,900,000
Total liabilities	55,936,000	63,998,000
Common stock warrant liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Common stock warrant liabilities	36,000	198,000
Common stock warrant liabilities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Common stock warrant liabilities	0	0
Common stock warrant liabilities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Common stock warrant liabilities	0	0
Common stock warrant liabilities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Common stock warrant liabilities	36,000	198,000
Contingent consideration liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration liabilities	55,900,000	63,800,000
Contingent consideration liabilities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration liabilities	0	0
Contingent consideration liabilities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration liabilities	0	0
Contingent consideration liabilities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration liabilities	55,900,000	63,800,000
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	34,634,000	7,485,000
Short-term fixed income securities	39,528,000	73,366,000
Commercial paper | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Short-term fixed income securities	0	0
Commercial paper | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	34,634,000	7,485,000
Short-term fixed income securities	39,528,000	73,366,000
Commercial paper | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Short-term fixed income securities	0	0
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	224,070,000	11,527,000
Money market funds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	224,070,000	11,527,000
Money market funds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents		0
Money market funds | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term fixed income securities	70,750,000	74,417,000
Corporate debt securities | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term fixed income securities	0	0
Corporate debt securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term fixed income securities	70,750,000	74,417,000
Corporate debt securities | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term fixed income securities	0	0
Certificate of deposits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term fixed income securities	39,940,000	41,302,000
Certificate of deposits | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term fixed income securities	0	0
Certificate of deposits | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term fixed income securities	39,940,000	41,302,000
Certificate of deposits | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term fixed income securities	$ 0	$ 0
ZX008
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Potential contingent consideration payment, minimum			$ 0
Potential contingent consideration payment, maximum			$ 75,000,000

Fair Value Measurements - Signi

Fair Value Measurements - Significant Inputs Used in Fair Value Measurement (Details) $ in Thousands	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 55,900
Discount Rate | Discounted cash flow | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input (percent)	0.065
Discount Rate | Discounted cash flow | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input (percent)	0.148
Discount Rate | Discounted cash flow | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input (percent)	0.098
Probability of payment | Discounted cash flow | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input (percent)	0
Probability of payment | Discounted cash flow | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input (percent)	0.851
Probability of payment | Discounted cash flow | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input (percent)	0.851
Contingent consideration liabilities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 55,900	$ 63,800
Contingent consideration liabilities | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair value	$ 55,900	$ 63,800

Fair Value Measurements - Recon

Fair Value Measurements - Reconciliation of Liabilities Measured at Fair Value Using Significant Unobservable Inputs (Details) - Contingent consideration liabilities - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 63,800	$ 78,200
Change in fair value	(7,900)	3,000
Settlements	0	(10,000)
Balance at end of period	$ 55,900	$ 71,200

Accrued and Other Current Lia_3

Accrued and Other Current Liabilities - Details of Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued clinical trial expenses	$ 14,215	$ 18,666
Accrued compensation	4,930	7,179
Other accrued liabilities	6,622	4,074
Common stock warrant liabilities	36	198
Accrued Liabilities and Other Current Liabilities	$ 25,803	$ 30,117

Leases - Narrative (Details)

Leases - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Feb. 29, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Aggregate lease payments	$ 15,745			$ 14,899
Short-term lease cost	157	$ 328
Cash paid for amounts included in measurement of lease liabilities	600	$ 300
Right-of-use asset obtained in exchange for new operating lease liabilities	$ 1,200
Weighted average remaining lease term	6 years 9 months 18 days
Weighted-average discount rate (percent)	6.20%
Maidenhead, United Kingdom Lease
Lessee, Lease, Description [Line Items]
Term of new lease			5 years
Aggregate lease payments			$ 1,500
Short-term Lease Terminated in March 2019
Lessee, Lease, Description [Line Items]
Short-term lease cost	$ 200

Leases - Information Related to

Leases - Information Related to Operating Leases (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Lease, Cost [Abstract]
Operating lease cost	$ 567	$ 499
Short-term lease cost	157	328
Sublease income	(115)	(145)
Total	$ 609	$ 682

Leases - Maturities of Lease Li

Leases - Maturities of Lease Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Operating Lease Liabilities, Payments Due [Abstract]
2020 (remaining 9 months)	$ 1,533
2020 (remaining 12 months)		$ 1,986
2021	2,292	1,957
2022	2,230	1,894
2023	2,287	1,951
2024	2,300	2,010
Thereafter	5,103	5,101
Total lease payments	15,745	14,899
Less imputed interest	(2,908)	(2,825)
Total operating lease liabilities	12,837	12,074
Assets and Liabilities, Lessee [Abstract]
Current portion of operating lease liabilities	1,383	1,322
Operating lease liabilities, net of current portion	11,454	10,752
Total operating lease liabilities	$ 12,837	$ 12,074

Stockholders' Equity and Stoc_3

Stockholders' Equity and Stock-Based Compensation - Additional Information (Details) $ / shares in Units, shares in Thousands, $ in Millions	1 Months Ended	13 Months Ended
	Mar. 31, 2020USD ($)$ / sharesshares	Mar. 31, 2020$ / sharesshares
Underwritten Public Offering
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued in public offering (shares)	9,798
Price per share (in usd per share) | $ / shares	$ 23.50	$ 23.50
Proceeds realized from offering | $	$ 221.7
Option to purchase additional shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued in public offering (shares)		1,278

Stockholders' Equity and Stoc_4

Stockholders' Equity and Stock-Based Compensation - Options Activity (Details) shares in Thousands	3 Months Ended
	Mar. 31, 2020$ / sharesshares
Shares (in thousands)
Options outstanding, beginning of period (in shares) | shares	4,253
Granted (in shares) | shares	841
Exercised (in shares) | shares	(230)
Canceled (in shares) | shares	(65)
Options outstanding, end of period (in shares) | shares	4,799
Weighted- Average Exercise Price per Share
Outstanding weighted average exercise price, beginning balance (in usd per share) | $ / shares	$ 29.59
Granted weighted average exercise price (in usd per share | $ / shares	30.11
Exercised weighted average exercise price (in usd per share | $ / shares	16.87
Canceled weighted average exercise price (in usd per share | $ / shares	37.07
Outstanding weighted average exercise price, ending balance (in usd per share | $ / shares	$ 30.19

Stockholders' Equity and Stoc_5

Stockholders' Equity and Stock-Based Compensation - Restricted Stock Unit Activity (Details) - Restricted stock units shares in Thousands	3 Months Ended
	Mar. 31, 2020$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at beginning of period (in shares) | shares	439
Granted (in shares) | shares	216
Vested (in shares) | shares	(66)
Canceled (in shares) | shares	(8)
Outstanding at end of period (in shares) | shares	581
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Nonvested at beginning of period - Weighted average fair value per share at grant date (in usd per share) | $ / shares	$ 36.97
Granted - Weighted average fair value per share at grant date (in usd per share) | $ / shares	27.36
Vested - Weighted average fair value per share at grant date (in usd per share) | $ / shares	48.41
Canceled - Weighted average fair value per share at grant date (in usd per share) | $ / shares	37.56
Nonvested at end of period - Weighted average fair value per share at grant date (in usd per share) | $ / shares	$ 32.11

Stockholders' Equity and Stoc_6

Stockholders' Equity and Stock-Based Compensation - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 6,394	$ 4,223
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	2,729	1,435
Selling, general and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 3,665	$ 2,788

Net Loss Per Share - Reconcilia

Net Loss Per Share - Reconciliation of Numerator and Denominators in Computing Net Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Net loss	$ (25,800)	$ (35,202)
Shares used in per share calculation (in shares)	48,185	42,236
Net loss per share, basic and diluted (in dollars per share)	$ (0.54)	$ (0.83)

Net Loss Per Share - Antidiluti

Net Loss Per Share - Antidilutive Securities (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share amount	4,963	4,039
Shares subject to outstanding stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share amount	4,450	3,716
Shares subject to outstanding restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share amount	485	295
Shares subject to outstanding warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share amount	28	28

United Kingdom (U.K.) Researc_2

United Kingdom (U.K.) Research and Development Incentives (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Operating Loss Carryforwards [Line Items]
Claim for refundable cash credit		$ 19.7
U.K. Tax Legislation | U.K. Tax Legislation
Operating Loss Carryforwards [Line Items]
Window to seek relief under U.K. tax legislature	2 years
Tax Year 2017
Operating Loss Carryforwards [Line Items]
Claim for refundable cash credit		9.9
Tax Year 2018
Operating Loss Carryforwards [Line Items]
Claim for refundable cash credit		$ 9.8