Atara Biotherapeutics (ATRA) 10-Q 9 Nov 17 2017 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Oct. 31, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q3
Trading Symbol	ATRA
Entity Registrant Name	Atara Biotherapeutics, Inc.
Entity Central Index Key	1,604,464
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		30,595,866

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 60,493	$ 47,968
Short-term investments	139,728	207,714
Restricted cash - short-term	194	194
Prepaid expenses and other current assets	5,802	4,677
Total current assets	206,217	260,553
Property and equipment, net	22,176	3,259
Restricted cash - long-term	1,200	0
Other assets	100	102
Total assets	229,693	263,914
Current liabilities:
Accounts payable	5,539	2,778
Accrued compensation	5,319	3,745
Accrued research and development expenses	3,810	2,408
Other accrued liabilities	1,848	744
Total current liabilities	16,516	9,675
Long-term liabilities	7,221	503
Total liabilities	23,737	10,178
Commitments and contingencies (Note 7)
Stockholders’ equity:
Common stock—$0.0001 par value, 500,000 shares authorized as of September 30, 2017 and December 31, 2016; 30,596 and 28,933 shares issued and outstanding as of September 30, 2017 and December 31, 2016, respectively	3	3
Additional paid-in capital	467,378	431,075
Accumulated other comprehensive loss	(88)	(183)
Accumulated deficit	(261,337)	(177,159)
Total stockholders’ equity	205,956	253,736
Total liabilities and stockholders’ equity	$ 229,693	$ 263,914

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	500,000	500,000
Common stock, shares issued	30,596	28,933
Common stock, shares outstanding	30,596	28,933

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Operating expenses:
Research and development	$ 20,598	$ 18,802	$ 56,435	$ 43,040
General and administrative	11,062	7,140	29,295	19,448
Total operating expenses	31,660	25,942	85,730	62,488
Loss from operations	(31,660)	(25,942)	(85,730)	(62,488)
Interest and other income, net	564	576	1,554	1,684
Loss before provision for income taxes	(31,096)	(25,366)	(84,176)	(60,804)
Provision for income taxes	0	7	2	10
Net loss	(31,096)	(25,373)	(84,178)	(60,814)
Other comprehensive loss:
Unrealized gain (loss) on available-for-sale securities	26	(158)	95	553
Comprehensive loss	$ (31,070)	$ (25,531)	$ (84,083)	$ (60,261)
Net loss per common share:
Basic and diluted net loss per common share	$ (1.02)	$ (0.88)	$ (2.84)	$ (2.12)
Weighted-average shares outstanding used to calculate basic and diluted net loss per common share	30,474	28,801	29,597	28,670

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating activities
Net loss	$ (84,178)	$ (60,814)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	17,003	15,128
Amortization of investment premiums and discounts	607	2,811
Depreciation expense	678	210
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,125)	(602)
Other assets	2	6
Accounts payable	(1)	3,018
Accrued compensation	1,574	532
Accrued research and development expenses	1,402	(3)
Other accrued liabilities	1,104	433
Long-term liabilities	370	420
Net cash used in operating activities	(62,564)	(38,861)
Investing activities
Purchases of short-term investments	(152,837)	(252,279)
Maturities of short-term investments	162,094	127,749
Sales of short-term investments	58,217	187,508
Purchases of property and equipment	(10,535)	(2,025)
Restricted cash	(1,200)	0
Net cash provided by investing activities	55,739	60,953
Financing activities
Proceeds from issuance of common stock from "at-the-market" facility, net	19,206	0
Taxes paid related to net share settlement of restricted stock units	(351)	(75)
Proceeds from employee stock awards	495	250
Net cash provided by financing activities	19,350	175
Increase in cash and cash equivalents	12,525	22,267
Cash and cash equivalents at beginning of period	47,968	23,746
Cash and cash equivalents at end of period	60,493	46,013
Non-cash investing and financing activities
Capitalized lease obligations	6,215	0
Property and equipment purchases included in liabilities	3,064	129
Interest capitalized during construction period for build-to-suit lease transaction	133	0
Issuance of common stock upon vesting of stock awards	0	60
Change in long-term liabilities related to non-vested stock awards	0	(60)
Supplemental cash flow disclosure
Cash paid for taxes	$ 0	$ 10

Description of Business

Description of Business	9 Months Ended
	Sep. 30, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Description of Business	1. Description of Business Atara Biotherapeutics, Inc. (“Atara”, “we”, “our” or “the Company”) was incorporated in August 2012 in Delaware. Atara is a cell therapy company developing novel treatments for patients with cancer and multiple sclerosis (MS). The Company’s “off-the-shelf”, or allogeneic, T-cells are engineered from donors with healthy immune function and allow for rapid delivery from inventory to patients without a requirement for pretreatment. Atara’s T-cell immunotherapies are designed to precisely recognize and eliminate cancerous or diseased cells without affecting normal, healthy cells. We licensed rights to T-cell product candidates from Memorial Sloan Kettering Cancer Center (“MSK”) in June 2015 and to know-how and technology from QIMR Berghofer Medical Research Institute (“QIMR Berghofer”) in October 2015 and September 2016. See Note 6 for further information.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and follow the requirements of the Securities and Exchange Commission (“SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP can be condensed or omitted. These condensed consolidated financial statements have been prepared on the same basis as the Company’s annual consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2016, and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, which are necessary for a fair statement of the Company’s consolidated financial information. The results of operations for the nine-month period ended September 30, 2017 are not necessarily indicative of the results to be expected for the full year or any other future period. The condensed consolidated balance sheet as of December 31, 2016 has been derived from audited consolidated financial statements at that date but does not include all of the information required by U.S. GAAP for complete consolidated financial statements. Significant Risks and Uncertainties We have incurred significant operating losses since inception and have relied on public and private equity financings to fund our operations. As of September 30, 2017, we had an accumulated deficit of $261.3 million. As we continue to incur losses, our transition to profitability will depend on the successful development, approval and commercialization of product candidates and on the achievement of sufficient revenues to support our cost structure. We may never achieve profitability, and unless and until we do, we will need to continue to raise additional capital. Management expects that our cash, cash equivalents and short-term investments as of September 30, 2017 will be sufficient to fund our planned operations into the first quarter of 2019. Concentration of Credit Risk and Other Uncertainties We place cash and cash equivalents in the custody of financial institutions that management believes are of high credit quality, the amount of which at times, may be in excess of the amount insured by the Federal Deposit Insurance Corporation. We also have short-term investments in money market funds, U.S. Treasury, government agency and corporate debt obligations, commercial paper and asset-backed securities, which can be subject to certain credit risk. However, we mitigate the risks by investing in high-grade instruments, limiting our exposure to any one issuer, and monitoring the ongoing creditworthiness of the financial institutions and issuers. We are subject to certain risks and uncertainties and believe that changes in any of the following areas could have a material adverse effect on future financial position or results of operations: our ability to obtain future financing; regulatory approval and market acceptance of, and reimbursement for, our product candidates, if approved; performance of third-party clinical research organizations and manufacturers upon which we rely; development of sales channels; protection of our intellectual property; litigation or claims against us based on intellectual property, patent, product, regulatory or other factors; and our ability to attract and retain employees necessary to support our growth. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates, assumptions, and judgments that affect the amounts reported in the financial statements and accompanying notes. Significant estimates relied upon in preparing these financial statements include estimates related to clinical trial and other accruals, stock-based compensation expense, construction costs and income taxes. Actual results could differ materially from those estimates. Leases We lease office space in multiple locations. In addition, we are constructing a manufacturing facility in Thousand Oaks, California under a non-cancelable lease agreement. The leases are reviewed for classification as operating or capital leases. For operating leases, rent is recognized on a straight-line basis over the lease period. For capital leases, we record the leased asset with a corresponding liability for principal and interest. Payments are recorded as reductions to these liabilities with interest being charged to interest expense in our statements of operations and comprehensive loss. We analyzed the nature of the renovations and our involvement during the construction period of our manufacturing facility and determined that we are the deemed “owner” of the construction project during the construction period. As a result, we are required to capitalize the fair value of the building as well as the construction costs incurred on our condensed consolidated balance sheet along with a corresponding financing liability for landlord-paid construction costs (i.e. “build-to-suit” accounting). Upon occupancy for build-to-suit leases, we are also required to assess whether the circumstances qualify for sale recognition under “sale-leaseback” accounting guidance. Recent Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842) In March 2016, the FASB issued ASU No. 2016-09, Improvements to Employee Share-Based Payment Accounting (Topic 718) In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments In November 2016, the FASB issued ASU No. 2016-18 Statement of Cash Flows (Topic 230): Restricted Cash In May 2017, the FASB issued ASU No. 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting.

Net Loss per Common Share

Net Loss per Common Share	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Net Loss per Common Share	3. Basic net loss per common share is calculated by dividing net loss by the weighted-average number of shares of common stock outstanding during the period, without consideration of common share equivalents. Diluted net loss per common share is computed by dividing net loss by the weighted-average number of shares of common stock and common share equivalents outstanding for the period. Common share equivalents are only included in the calculation of diluted net loss per common share when their effect is dilutive. Potential dilutive securities, which include unvested restricted stock awards (“RSAs”), unvested restricted stock units (“RSUs”), vested and unvested options to purchase common stock and shares to be issued under our employee stock purchase plan (“ESPP”) have been excluded from the computation of diluted net loss per share as the effect is antidilutive. Therefore, the denominator used to calculate both basic and diluted net loss per common share is the same in all periods presented. The following table represents the potential common shares issuable pursuant to outstanding securities as of the related period end dates that were excluded from the computation of diluted net loss per common share as their inclusion would have an antidilutive effect: As of September 30, 2017 2016 Unvested RSAs — 18,510 Unvested RSUs 1,735,999 1,371,269 Vested and unvested options 4,910,449 3,744,176 ESPP share purchase rights 32,205 15,888 Total 6,678,653 5,149,843

Financial Instruments

Financial Instruments	9 Months Ended
	Sep. 30, 2017
Financial Instruments Disclosure [Abstract]
Financial Instruments	4. Our financial assets are measured at fair value on a recurring basis using the following hierarchy to prioritize valuation inputs, Level 1: Quoted prices in active markets for identical assets or liabilities that we have the ability to access Level 2: Observable market based inputs or unobservable inputs that are corroborated by market data such as quoted prices, interest rates and yield curves Level 3: Inputs that are unobservable data points that are not corroborated by market data We review the fair value hierarchy classification on a quarterly basis. Changes in the ability to observe valuation inputs may result in a reclassification of levels of certain securities within the fair value hierarchy. We recognize transfers into and out of levels within the fair value hierarchy in the period in which the actual event or change in circumstances that caused the transfer occurs. There have been no transfers between Level 1, Level 2 and Level 3 in any periods presented. Financial assets and liabilities are considered Level 2 when their fair values are determined using inputs that are observable in the market or can be derived principally from or corroborated by observable market data such as pricing for similar securities, recently executed transactions, cash flow models with yield curves, and benchmark securities. In addition, Level 2 financial instruments are valued using comparisons to like-kind financial instruments and models that use readily observable market data as their basis. U.S. Treasury, government agency and corporate debt obligations, commercial paper and asset-backed securities are valued primarily using market prices of comparable securities, bid/ask quotes, interest rate yields and prepayment spreads and are included in Level 2. Financial assets and liabilities are considered Level 3 when their fair values are determined using pricing models, discounted cash flow methodologies, or similar techniques, and at least one significant model assumption or input is unobservable. We have no Level 3 financial assets or liabilities. The following tables summarize the estimated fair value and related valuation input hierarchy of our available-for-sale securities as of each period end: Total Total Total Total Amortized Unrealized Unrealized Estimated As of September 30, 2017: Input Level Cost Gain Loss Fair Value (in thousands) Money market funds Level 1 $ 47,593 $ — $ — $ 47,593 U.S. Treasury obligations Level 2 51,692 2 (16 ) 51,678 Government agency obligations Level 2 4,760 1 (6 ) 4,755 Corporate debt obligations Level 2 82,402 9 (69 ) 82,342 Commercial paper Level 2 2,085 — — 2,085 Asset-backed securities Level 2 7,976 — (9 ) 7,967 Total available-for-sale securities 196,508 12 (100 ) 196,420 Less amounts classified as cash equivalents (56,692 ) — — (56,692 ) Amounts classified as short-term investments $ 139,816 $ 12 $ (100 ) $ 139,728 Total Total Total Total Amortized Unrealized Unrealized Estimated As of December 31, 2016: Input Level Cost Gain Loss Fair Value (in thousands) Money market funds Level 1 $ 28,816 $ — $ — $ 28,816 U.S. Treasury obligations Level 2 65,403 3 (21 ) 65,385 Government agency obligations Level 2 23,860 5 (5 ) 23,860 Corporate debt obligations Level 2 113,649 8 (172 ) 113,485 Commercial paper Level 2 699 — — 699 Asset-backed securities Level 2 13,414 4 (6 ) 13,412 Total available-for-sale securities 245,841 20 (204 ) 245,657 Less amounts classified as cash equivalents (37,944 ) — 1 (37,943 ) Amounts classified as short-term investments $ 207,897 $ 20 $ (203 ) $ 207,714 The amortized cost and fair value of our available-for-sale securities by contractual maturity were as follows: As of September 30, 2017 As of December 31, 2016 Amortized Estimated Amortized Estimated Cost Fair Value Cost Fair Value (in thousands) (in thousands) Maturing within one year $ 171,265 $ 171,220 $ 198,022 $ 197,956 Maturing in one to five years 25,243 25,200 47,819 47,701 Total available-for-sale securities $ 196,508 $ 196,420 $ 245,841 $ 245,657 As of September 30, 2017, certain available-for-sale securities had been in a continuous unrealized loss position, each for less than twelve months. As of this date, no significant facts or circumstances were present to indicate a deterioration in the creditworthiness of the respective issuers, and the Company has no requirement or intention to sell these securities before maturity or recovery of their amortized cost basis. During , we did not recognize any other-than-temporary impairment losses. In addition, restricted cash collateralized by money market funds is a financial asset measured at fair value and is a Level 1 financial instrument under the fair value hierarchy. As of September 30, 2017 and December 31, 2016, restricted cash totaled $1.4 million and $0.2 million, respectively.

Property and Equipment

Property and Equipment	9 Months Ended
	Sep. 30, 2017
Property Plant And Equipment [Abstract]
Property and Equipment	5. Property and Equipment Property and equipment consisted of the following as of each period end: September 30, December 31, 2017 2016 (in thousands) Construction in progress $ 19,643 $ 970 Lab equipment 2,375 1,506 Leasehold improvements 623 580 Furniture and fixtures 536 526 Computer equipment and software 66 66 23,243 3,648 Less accumulated depreciation and amortization (1,067 ) (389 ) Property and equipment, net $ 22,176 $ 3,259 Property and equipment includes lab equipment, furniture and fixtures, computer equipment and software, which are depreciated over the estimated useful lives of the assets, ranging from three to five years. Leasehold improvements are amortized over the lesser of the useful life of the leasehold improvements or the lease term. Construction in progress represents capitalized costs for our manufacturing facility in Thousand Oaks, California. Depreciation and amortization expense was $0.3 million and $0.1 million for the three months ended September 30, 2017 and 2016, and $0.7 million and $0.2 million for the nine months ended September 30, 2017 and 2016, respectively.

License and Collaboration Agree

License and Collaboration Agreements	9 Months Ended
	Sep. 30, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
License and Collaboration Agreements	6. License and Collaboration Agreements MSK Agreements – In September 2014, we entered into an exclusive option agreement with MSK under which we had the right to acquire the exclusive worldwide license rights to three clinical stage T-cell therapies from MSK. In exchange for the option, we paid $1.25 million in cash and issued 59,761 shares of our common stock to MSK. At the time of issuance, we estimated the fair value of the stock issued to MSK to be $0.75 million. The total of $2.0 million was recorded as research and development expense in our statements of operations and comprehensive loss. In June 2015, we exercised an option to enter into an exclusive license agreement with MSK for three clinical stage T-cell therapies. In connection with the execution of the license agreement, we paid $4.5 million in cash to MSK, which was recorded as research and development expense in our condensed consolidated statement of operations and comprehensive loss. We are required to make additional payments of up to $33.0 million to MSK based on achievement of specified regulatory and sales-related milestones, mid-single-digit percentage tiered royalty payments based on In addition, under certain circumstances, we are required to make certain minimum annual royalty payments to MSK, which are creditable against earned royalties owed for the same annual period. We are also required to pay a low double-digit percentage of any consideration we receive for sublicensing the licensed rights. QIMR Berghofer Agreements – In October 2015, we entered into an exclusive license agreement and a research and development collaboration agreement with QIMR Berghofer. Under the terms of the license agreement, we obtained an exclusive, worldwide license to develop and commercialize allogeneic cytotoxic T-lymphocyte (“CTL”) therapy programs utilizing technology and know-how developed by QIMR Berghofer. In consideration for the exclusive license, we paid $3.0 million in cash to QIMR Berghofer, which was recorded as research and development expense in our statement of operations and comprehensive loss in the fourth quarter of 2015. In September 2016, the exclusive license agreement and research and development collaboration agreement were amended and restated. Under the amended and restated agreements, we obtained an exclusive, worldwide license to develop and commercialize additional CTL programs as well as the option to license additional technology in exchange for $3.3 million in cash, which was recorded as research and development expense in our statement of operations and comprehensive loss in the third quarter of 2016 and paid in October 2016. The amended and restated license agreement also provides for various milestone and royalty payments to QIMR Berghofer based on future product sales, if any. Under the terms of the amended and restated research and development collaboration agreement, we are also required to reimburse the cost of agreed-upon development activities related to programs developed under the collaboration. These payments are expensed on a straight-line basis over the related development periods and recorded in research and development expense in our condensed consolidated statements of operations and comprehensive loss. The agreement also provides for various milestone payments to QIMR Berghofer based on achievement of certain developmental and regulatory milestones. Milestones and royalties under each of the above agreements are contingent upon future events and will be recorded as expense when it is probable that the milestones will be achieved or royalties are due. As of September 30, 2017 and December 31, 2016, there were no outstanding obligations for milestones and royalties. Amgen License Agreements – In September 2012, we entered into license agreements with Amgen, Inc., for several molecular programs, including PINTA745, ATA842 and STM434. In December 2015, we announced the suspension of further development of PINTA745, and in June 2016, we returned the rights related to this and the ATA842 program to Amgen. In October 2017, we returned all remaining rights under the license agreements to Amgen.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies License and Collaboration Agreements Certain potential payments related to our license and collaboration agreements, including milestone and royalty payments, are detailed in Note 6. As the achievement of these milestones and royalties are currently not fixed and determinable, such commitments have not been included in our condensed consolidated balance sheets. Other Research and Development Agreements We may enter into contracts in the normal course of business with clinical research organizations for clinical trials, with contract manufacturing clinical supplies, and with other vendors for pre-clinical studies, supplies and other services for our operating purposes. These contracts generally provide for termination on Operating Leases We lease our corporate headquarters in South San Francisco, California under a non-cancellable lease agreement that expires in April 2021. In connection with the lease, we were required to issue a letter of credit in the amount of $0.2 million to the landlord, which expires in December 2017 and is classified as restricted cash in our condensed consolidated balance sheet. We also lease office space in Westlake Village, California under a lease agreement that expires in April 2019. Rent expense was $0.4 million and $0.3 million for the three months ended September 30, 2017 and 2016, respectively and $1.0 million and $0.9 million, for the nine months ended September 30, 2017 and 2016, respectively. Financing Obligation—Build-to-Suit Lease In February 2017, we entered into a lease agreement for approximately 90,580 square feet of office, lab and cellular therapy manufacturing space in Thousand Oaks, California. The initial 15-year term of the lease commences upon the substantial completion of landlord’s work as defined under the agreement. The contractual obligations during the initial term are $16.4 million in aggregate. Based on the terms of the lease agreement and due to our involvement in certain aspects of the construction, we have been deemed the owner of the building (for accounting purposes only) during the construction period in accordance with U.S. GAAP. Under this build-to-suit lease arrangement, we recognize construction in progress based on all construction costs incurred by both us and the landlord. We also recognize a financing obligation equal to all costs funded by the landlord. As of September 30, 2017, we have recorded $6.2 million of construction in progress relating to landlord’s costs of the building incurred through that date, and have recognized a corresponding long-term financing obligation for the same amount. In addition, we have recorded $12.1 million of construction in progress for construction costs incurred by us and $0.1 million of capitalized interest during the construction period through September 30, 2017. Further, we recorded ground lease expense of $88,000 and $205,000 for the three and nine months ended September 30, 2017 respectively, in our condensed consolidated statement of operations and comprehensive loss, representing the estimated cost of renting the land during the construction period. Indemnification Agreements In the normal course of business, we enter into contracts and agreements that contain a variety of representations and warranties and provide for indemnification for certain liabilities. The exposure under these agreements is unknown because it involves claims that may be made against us in the future but have not yet been made. To date, we have not paid any claims or been required to defend any action related to our indemnification obligations. However, we may record charges in the future as a result of these indemnification obligations. We also have indemnification obligations to our directors and executive officers for specified events or occurrences, subject to some limits, while they are serving at our request in such capacities. There have been no claims to date and we believe the fair value of these indemnification agreements is minimal. Accordingly, we did not record liabilities for these agreements as of September 30, 2017 and December 31, 2016. Contingencies From time to time, we may be involved in legal proceedings, as well as demands, claims and threatened litigation, which arise in the normal course of our business or otherwise. The ultimate outcome of any litigation is uncertain and unfavorable outcomes could have a negative impact on our results of operations and financial condition. Regardless of outcome, litigation can have an adverse impact on us because of the defense costs, diversion of management resources and other factors. We are not currently involved in any material legal proceedings.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stockholders' Equity	8. Stockholders’ Equity Equity Offering In March 2017, we entered into a sales agreement (the “ATM facility”) with Cowen and Company, LLC (“Cowen”) under which we may offer and sell, in our sole discretion, shares of our common stock, having an aggregate offering price of up to $75.0 million through Cowen, as our sales agent. We will pay Cowen a commission of up to 3.0% of the gross sales proceeds of any common stock sold under the ATM facility. The issuance and sale of these shares by us pursuant to the ATM facility are deemed “at the market” offerings and are available under the Securities Act of 1933, as amended. During the three and nine-months ended September 30, 2017, we sold an aggregate of 655,876 and 1,349,865 shares of common stock, respectively, under the ATM facility, at an average price of approximately $15.55 per share and $14.82 per share, respectively, for gross proceeds of $10.2 million and $20.0 million, respectively and net proceeds of $9.9 million and $19.2 million, respectively, after deducting commissions and other offering expenses. As of September 30, 2017, $55.0 million of common stock remained available to be sold under this facility, subject to certain conditions as specified in the agreement. Equity Incentive Plan Under the terms of the 2014 Equity Incentive Plan (“2014 EIP”), we may grant options, RSAs and RSUs to employees, directors, consultants and other service providers. As of September 30, 2017, a total of 10,310,669 shares of common stock were reserved for issuance under the 2014 Plan, of which 3,921,737 shares were available for future grant and 6,388,932 shares were subject to outstanding options and RSUs. Restricted Stock Units The following is a summary of RSU activity under our 2014 EIP: RSUs Shares Weighted Average Grant Date Fair Value Unvested as of December 31, 2016 1,286,262 $ 16.61 Granted 782,413 $ 15.07 Forfeited (50,063 ) $ 15.41 Vested (282,613 ) $ 12.02 Unvested as of September 30, 2017 1,735,999 $ 16.70 Vested and unreleased 17,484 Outstanding as of September 30, 2017 1,753,483 The fair value of RSUs is determined as the closing stock price on the date of grant. The weighted average grant date fair value of RSUs granted was $15.07 and $17.83 for the nine months ended September 30, 2017 and 2016, respectively. As of September 30, 2017, there was $22.8 million of unrecognized stock-based compensation expense related to RSUs that is expected to be recognized over a weighted average period of 2.8 years. The aggregate intrinsic value of the RSUs outstanding as of September 30, 2017 was $29.0 million. Under our RSU net settlement procedures, we withhold shares at settlement to cover the minimum payroll withholding tax obligations. During the nine months ended September 30, 2017, we settled 290,534 RSUs, of which 51,592 RSUs were net settled by withholding 21,895 shares. The value of the RSUs withheld was $0.4 million, based on the closing price of our common stock on the settlement date. During the nine months ended September 30, 2016, we settled 153,719 RSUs, of which 10,898 RSUs were net settled by withholding 4,251 shares. The value of the RSUs withheld was $75,000, based on the closing price of our common stock on the settlement date. The value of RSUs withheld in each period was remitted to the appropriate taxing authorities and has been reflected as a financing activity in our condensed consolidated statements of cash flows. Stock Options The following is a summary of stock option activity under our 2014 EIP: Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2016 3,733,847 $ 24.14 Granted 1,155,900 $ 15.99 Exercised — $ — Forfeited or expired (254,298 ) $ 25.40 Outstanding as of September 30, 2017 4,635,449 $ 22.04 5.3 $ 4,102 Vested and expected to vest as of September 30, 2017 4,635,449 $ 22.04 5.3 $ 4,102 Exercisable as of September 30, 2017 1,887,909 $ 23.77 4.6 $ 1,919 Aggregate intrinsic value represents the difference between the closing stock price of our common stock on September 30, 2017 and the exercise price of outstanding, in-the-money options. As of September 30, 2017, there was $32.6 million of unrecognized stock-based compensation expense related to stock options that is expected to be recognized over a weighted average period of 2.6 years. Options for 18,947 shares of our common stock were exercised during the nine months ended September 30, 2016, with an intrinsic value of $0.2 million. No options were exercised during the nine months ended September 30, 2017. As we believe it is more likely than not that no stock option related tax benefits will be realized, we do not record any net tax benefits related to exercised options. The fair value of each option issued was estimated at the date of grant using the Black-Scholes valuation model. The following table summarizes the weighted-average assumptions used as inputs to the Black-Scholes model, and resulting weighted-average grant date fair values of stock options granted to employees during the periods indicated: Nine months ended September 30, 2017 Nine months ended September 30, 2016 Assumptions: Expected term (years) 4.5 4.5 Expected volatility 69.1 % 69.0 % Risk-free interest rate 1.8 % 1.3 % Expected dividend yield 0.0 % 0.0 % Fair Value: Weighted-average estimated grant date fair value per share $ 8.88 $ 11.23 Options granted 1,155,900 795,700 Total estimated grant date fair value $ 10,264,000 $ 8,935,000 There were no options granted to consultants in the nine months ended September 30, 2017. 9,000 options were granted to consultants in the nine months ended September 30, 2016. The estimated fair value of stock options that vested in the nine months ended September 30, 2017 and 2016 was $10.9 million and $10.4 million, respectively. Employee Stock Purchase Plan As of September 30, 2017, there were 827,630 shares available for purchase under the 2014 Employee Stock Purchase Plan (“2014 ESPP”). The Company recorded $0.4 million and $0.3 million of expense related to the 2014 ESPP in the nine months ended September 30, 2017 and 2016, respectively. 43,962 shares were purchased under the ESPP during the nine months ended September 30, 2017. There were no purchases of shares during the nine months ended September 30, 2016. Options issued outside the 2014 EIP During the three and nine months ended September 30, 2017, we granted 145,000 options and 275,000 options, respectively, at weighted average exercise prices of $13.65 per share and $13.96 per share, respectively, outside of our 2014 EIP. These options have terms similar to the options granted under the 2014 EIP. The weighted average grant date fair value of such grants were $1.2 million and $2.2 million, respectively. No options were granted outside the 2014 EIP during the three and nine months ended September 30, 2016. Reserved Shares The following shares of common stock were reserved for future issuance as of September 30, 2017: Total Shares Reserved 2014 Equity Incentive Plan 10,310,669 2014 Employee Stock Purchase Plan 827,629 Options issued outside the 2014 EIP 275,000 Total reserved shares of common stock 11,413,298 Stock-based Compensation Expense Total stock-based compensation expense related to all employee and non-employee stock awards was as follows: Three Nine months ended September 30, 2017 2016 2017 2016 (in thousands) (in thousands) Research and development $ 2,136 $ 2,551 $ 6,260 $ 7,231 General and administrative 3,864 2,718 10,743 7,897 Total stock-based compensation expense $ 6,000 $ 5,269 $ 17,003 $ 15,128

Summary of Significant Accoun14

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and follow the requirements of the Securities and Exchange Commission (“SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP can be condensed or omitted. These condensed consolidated financial statements have been prepared on the same basis as the Company’s annual consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2016, and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, which are necessary for a fair statement of the Company’s consolidated financial information. The results of operations for the nine-month period ended September 30, 2017 are not necessarily indicative of the results to be expected for the full year or any other future period. The condensed consolidated balance sheet as of December 31, 2016 has been derived from audited consolidated financial statements at that date but does not include all of the information required by U.S. GAAP for complete consolidated financial statements.
Significant Risks and Uncertainties	Significant Risks and Uncertainties We have incurred significant operating losses since inception and have relied on public and private equity financings to fund our operations. As of September 30, 2017, we had an accumulated deficit of $261.3 million. As we continue to incur losses, our transition to profitability will depend on the successful development, approval and commercialization of product candidates and on the achievement of sufficient revenues to support our cost structure. We may never achieve profitability, and unless and until we do, we will need to continue to raise additional capital. Management expects that our cash, cash equivalents and short-term investments as of September 30, 2017 will be sufficient to fund our planned operations into the first quarter of 2019.
Concentration of Credit Risk and Other Uncertainties	Concentration of Credit Risk and Other Uncertainties We place cash and cash equivalents in the custody of financial institutions that management believes are of high credit quality, the amount of which at times, may be in excess of the amount insured by the Federal Deposit Insurance Corporation. We also have short-term investments in money market funds, U.S. Treasury, government agency and corporate debt obligations, commercial paper and asset-backed securities, which can be subject to certain credit risk. However, we mitigate the risks by investing in high-grade instruments, limiting our exposure to any one issuer, and monitoring the ongoing creditworthiness of the financial institutions and issuers. We are subject to certain risks and uncertainties and believe that changes in any of the following areas could have a material adverse effect on future financial position or results of operations: our ability to obtain future financing; regulatory approval and market acceptance of, and reimbursement for, our product candidates, if approved; performance of third-party clinical research organizations and manufacturers upon which we rely; development of sales channels; protection of our intellectual property; litigation or claims against us based on intellectual property, patent, product, regulatory or other factors; and our ability to attract and retain employees necessary to support our growth.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates, assumptions, and judgments that affect the amounts reported in the financial statements and accompanying notes. Significant estimates relied upon in preparing these financial statements include estimates related to clinical trial and other accruals, stock-based compensation expense, construction costs and income taxes. Actual results could differ materially from those estimates.
Leases	Leases We lease office space in multiple locations. In addition, we are constructing a manufacturing facility in Thousand Oaks, California under a non-cancelable lease agreement. The leases are reviewed for classification as operating or capital leases. For operating leases, rent is recognized on a straight-line basis over the lease period. For capital leases, we record the leased asset with a corresponding liability for principal and interest. Payments are recorded as reductions to these liabilities with interest being charged to interest expense in our statements of operations and comprehensive loss. We analyzed the nature of the renovations and our involvement during the construction period of our manufacturing facility and determined that we are the deemed “owner” of the construction project during the construction period. As a result, we are required to capitalize the fair value of the building as well as the construction costs incurred on our condensed consolidated balance sheet along with a corresponding financing liability for landlord-paid construction costs (i.e. “build-to-suit” accounting). Upon occupancy for build-to-suit leases, we are also required to assess whether the circumstances qualify for sale recognition under “sale-leaseback” accounting guidance.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842) In March 2016, the FASB issued ASU No. 2016-09, Improvements to Employee Share-Based Payment Accounting (Topic 718) In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses: Measurement of Credit Losses on Financial Instruments In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments In November 2016, the FASB issued ASU No. 2016-18 Statement of Cash Flows (Topic 230): Restricted Cash In May 2017, the FASB issued ASU No. 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting.

Net Loss per Common Share (Tabl

Net Loss per Common Share (Tables)	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Antidilutive Securities Excluded From Computation of Diluted Net Loss per Common Share	The following table represents the potential common shares issuable pursuant to outstanding securities as of the related period end dates that were excluded from the computation of diluted net loss per common share as their inclusion would have an antidilutive effect: As of September 30, 2017 2016 Unvested RSAs — 18,510 Unvested RSUs 1,735,999 1,371,269 Vested and unvested options 4,910,449 3,744,176 ESPP share purchase rights 32,205 15,888 Total 6,678,653 5,149,843

Financial Instruments (Tables)

Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2017
Financial Instruments Disclosure [Abstract]
Estimated Fair Value and Related Valuation Input Hierarchy of Available-for-Sale Securities Measured on Recurring Basis	Our financial assets are measured at fair value on a recurring basis using the following hierarchy to prioritize valuation inputs, Level 1: Quoted prices in active markets for identical assets or liabilities that we have the ability to access Level 2: Observable market based inputs or unobservable inputs that are corroborated by market data such as quoted prices, interest rates and yield curves Level 3: Inputs that are unobservable data points that are not corroborated by market data We review the fair value hierarchy classification on a quarterly basis. Changes in the ability to observe valuation inputs may result in a reclassification of levels of certain securities within the fair value hierarchy. We recognize transfers into and out of levels within the fair value hierarchy in the period in which the actual event or change in circumstances that caused the transfer occurs. There have been no transfers between Level 1, Level 2 and Level 3 in any periods presented. Financial assets and liabilities are considered Level 2 when their fair values are determined using inputs that are observable in the market or can be derived principally from or corroborated by observable market data such as pricing for similar securities, recently executed transactions, cash flow models with yield curves, and benchmark securities. In addition, Level 2 financial instruments are valued using comparisons to like-kind financial instruments and models that use readily observable market data as their basis. U.S. Treasury, government agency and corporate debt obligations, commercial paper and asset-backed securities are valued primarily using market prices of comparable securities, bid/ask quotes, interest rate yields and prepayment spreads and are included in Level 2. Financial assets and liabilities are considered Level 3 when their fair values are determined using pricing models, discounted cash flow methodologies, or similar techniques, and at least one significant model assumption or input is unobservable. We have no Level 3 financial assets or liabilities. The following tables summarize the estimated fair value and related valuation input hierarchy of our available-for-sale securities as of each period end: Total Total Total Total Amortized Unrealized Unrealized Estimated As of September 30, 2017: Input Level Cost Gain Loss Fair Value (in thousands) Money market funds Level 1 $ 47,593 $ — $ — $ 47,593 U.S. Treasury obligations Level 2 51,692 2 (16 ) 51,678 Government agency obligations Level 2 4,760 1 (6 ) 4,755 Corporate debt obligations Level 2 82,402 9 (69 ) 82,342 Commercial paper Level 2 2,085 — — 2,085 Asset-backed securities Level 2 7,976 — (9 ) 7,967 Total available-for-sale securities 196,508 12 (100 ) 196,420 Less amounts classified as cash equivalents (56,692 ) — — (56,692 ) Amounts classified as short-term investments $ 139,816 $ 12 $ (100 ) $ 139,728 Total Total Total Total Amortized Unrealized Unrealized Estimated As of December 31, 2016: Input Level Cost Gain Loss Fair Value (in thousands) Money market funds Level 1 $ 28,816 $ — $ — $ 28,816 U.S. Treasury obligations Level 2 65,403 3 (21 ) 65,385 Government agency obligations Level 2 23,860 5 (5 ) 23,860 Corporate debt obligations Level 2 113,649 8 (172 ) 113,485 Commercial paper Level 2 699 — — 699 Asset-backed securities Level 2 13,414 4 (6 ) 13,412 Total available-for-sale securities 245,841 20 (204 ) 245,657 Less amounts classified as cash equivalents (37,944 ) — 1 (37,943 ) Amounts classified as short-term investments $ 207,897 $ 20 $ (203 ) $ 207,714
Amortized Cost and Fair Value of Available for Sale Securities by Contractual Maturity	The amortized cost and fair value of our available-for-sale securities by contractual maturity were as follows: As of September 30, 2017 As of December 31, 2016 Amortized Estimated Amortized Estimated Cost Fair Value Cost Fair Value (in thousands) (in thousands) Maturing within one year $ 171,265 $ 171,220 $ 198,022 $ 197,956 Maturing in one to five years 25,243 25,200 47,819 47,701 Total available-for-sale securities $ 196,508 $ 196,420 $ 245,841 $ 245,657

Property and Equipment (Tables)

Property and Equipment (Tables)	9 Months Ended
	Sep. 30, 2017
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consisted of the following as of each period end: September 30, December 31, 2017 2016 (in thousands) Construction in progress $ 19,643 $ 970 Lab equipment 2,375 1,506 Leasehold improvements 623 580 Furniture and fixtures 536 526 Computer equipment and software 66 66 23,243 3,648 Less accumulated depreciation and amortization (1,067 ) (389 ) Property and equipment, net $ 22,176 $ 3,259

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of RSU Activity	The following is a summary of RSU activity under our 2014 EIP: RSUs Shares Weighted Average Grant Date Fair Value Unvested as of December 31, 2016 1,286,262 $ 16.61 Granted 782,413 $ 15.07 Forfeited (50,063 ) $ 15.41 Vested (282,613 ) $ 12.02 Unvested as of September 30, 2017 1,735,999 $ 16.70 Vested and unreleased 17,484 Outstanding as of September 30, 2017 1,753,483
Summary of Stock Option Activity	The following is a summary of stock option activity under our 2014 EIP: Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2016 3,733,847 $ 24.14 Granted 1,155,900 $ 15.99 Exercised — $ — Forfeited or expired (254,298 ) $ 25.40 Outstanding as of September 30, 2017 4,635,449 $ 22.04 5.3 $ 4,102 Vested and expected to vest as of September 30, 2017 4,635,449 $ 22.04 5.3 $ 4,102 Exercisable as of September 30, 2017 1,887,909 $ 23.77 4.6 $ 1,919
Summary of Options Estimated with Weighted Average	The fair value of each option issued was estimated at the date of grant using the Black-Scholes valuation model. The following table summarizes the weighted-average assumptions Nine months ended September 30, 2017 Nine months ended September 30, 2016 Assumptions: Expected term (years) 4.5 4.5 Expected volatility 69.1 % 69.0 % Risk-free interest rate 1.8 % 1.3 % Expected dividend yield 0.0 % 0.0 % Fair Value: Weighted-average estimated grant date fair value per share $ 8.88 $ 11.23 Options granted 1,155,900 795,700 Total estimated grant date fair value $ 10,264,000 $ 8,935,000
Schedule of Common Stock Reserved for Future Issuance	The following shares of common stock were reserved for future issuance as of September 30, 2017: Total Shares Reserved 2014 Equity Incentive Plan 10,310,669 2014 Employee Stock Purchase Plan 827,629 Options issued outside the 2014 EIP 275,000 Total reserved shares of common stock 11,413,298
Schedule of Stock-based Compensation, Related to Employee and Nonemployee Stock Awards	Total stock-based compensation expense related to all employee and non-employee stock awards was as follows: Three Nine months ended September 30, 2017 2016 2017 2016 (in thousands) (in thousands) Research and development $ 2,136 $ 2,551 $ 6,260 $ 7,231 General and administrative 3,864 2,718 10,743 7,897 Total stock-based compensation expense $ 6,000 $ 5,269 $ 17,003 $ 15,128

Description of Business (Detail

Description of Business (Detail)	9 Months Ended
	Sep. 30, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Entity incorporation state	Delaware
Entity incorporation date	Aug. 1, 2012

Summary of Significant Accoun20

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Accumulated deficit	$ 261,337	$ 177,159

Net Loss per Common Share - Ant

Net Loss per Common Share - Antidilutive Securities Excluded From Computation of Diluted Net Loss per Common Share (Detail) - shares	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	6,678,653	5,149,843
Unvested RSAs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	0	18,510
Unvested RSUs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	1,735,999	1,371,269
Vested and Unvested Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	4,910,449	3,744,176
ESPP Share Purchase Rights
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	32,205	15,888

Financial Instruments - Summary

Financial Instruments - Summary of Estimated Fair Value and Related Valuation Input Hierarchy of Available-for-Sale Securities (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	$ 196,508	$ 245,841
Total Unrealized Gain	12	20
Total Unrealized Loss	(100)	(204)
Total Fair Value	196,420	245,657
Money Market Funds | Level 1
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	47,593	28,816
Total Unrealized Gain	0	0
Total Unrealized Loss	0	0
Total Fair Value	47,593	28,816
U.S. Treasury Obligations | Level 2
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	51,692	65,403
Total Unrealized Gain	2	3
Total Unrealized Loss	(16)	(21)
Total Fair Value	51,678	65,385
Government Agency Obligations | Level 2
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	4,760	23,860
Total Unrealized Gain	1	5
Total Unrealized Loss	(6)	(5)
Total Fair Value	4,755	23,860
Corporate Debt Obligations | Level 2
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	82,402	113,649
Total Unrealized Gain	9	8
Total Unrealized Loss	(69)	(172)
Total Fair Value	82,342	113,485
Commercial Paper | Level 2
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	2,085	699
Total Unrealized Gain	0	0
Total Unrealized Loss	0	0
Total Fair Value	2,085	699
Asset-Backed Securities | Level 2
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	7,976	13,414
Total Unrealized Gain	0	4
Total Unrealized Loss	(9)	(6)
Total Fair Value	7,967	13,412
Amounts Classified As Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	56,692	37,944
Total Unrealized Gain	0	0
Total Unrealized Loss	0	(1)
Total Fair Value	56,692	37,943
Amounts Classified As Short-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	139,816	207,897
Total Unrealized Gain	12	20
Total Unrealized Loss	(100)	(203)
Total Fair Value	$ 139,728	$ 207,714

Financial Instruments - Amortiz

Financial Instruments - Amortized Cost and Fair Value of Available-for-Sale Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Amortized cost
Maturing within one year, Amortized cost	$ 171,265	$ 198,022
Maturing in one to five years, Amortized cost	25,243	47,819
Total available-for-sale securities, Amortized cost	196,508	245,841
Estimated Fair value
Maturing within one year, Estimated fair value	171,220	197,956
Maturing in one to five years, Estimated fair value	25,200	47,701
Total available-for-sale securities, Estimated fair value	$ 196,420	$ 245,657

Financial Instruments - Additio

Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Financial Instruments Disclosure [Abstract]
Restricted cash	$ 1.4	$ 0.2

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 23,243	$ 3,648
Less accumulated depreciation and amortization	(1,067)	(389)
Property and equipment, net	22,176	3,259
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	19,643	970
Lab Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,375	1,506
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	623	580
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	536	526
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 66	$ 66

Property and Equipment - Additi

Property and Equipment - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Property Plant And Equipment [Line Items]
Depreciation and amortization expense	$ 0.3	$ 0.1	$ 0.7	$ 0.2
Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life			3 years
Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life			5 years

License and Collaboration Agr27

License and Collaboration Agreements - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended			9 Months Ended
	Sep. 30, 2014	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Related Party Transaction [Line Items]
Payments under exclusive option license agreement	$ 1,250,000
Share issued under the agreements	59,761
Issuance of common stock related to technology licensing option	$ 750,000
Research and development expense	$ 2,000,000	$ 20,598,000	$ 18,802,000		$ 56,435,000	$ 43,040,000
Payments under license agreement					4,500,000
Potential milestone payments payable		33,000,000			33,000,000
Contractual obligations due MSK and QIMR		$ 0			$ 0		$ 0
QIMR Berghofer | License Agreement
Related Party Transaction [Line Items]
Research and development expense			$ 3,300,000
Payments under license agreement				$ 3,000,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	1 Months Ended	3 Months Ended		9 Months Ended
	Feb. 28, 2017USD ($)ft²	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Dec. 31, 2016USD ($)
Loss Contingencies [Line Items]
Accrued termination charges		$ 0		$ 0		$ 0
Letter of credit issued		1,400,000		1,400,000		200,000
Rental expenses		400,000	$ 300,000	1,000,000	$ 900,000
Letter of credit issued, classified as long-term restricted cash		1,200,000		1,200,000		0
Ground lease expense		88,000		205,000
Liabilities related to indemnification agreements		0		0		$ 0
Building
Loss Contingencies [Line Items]
Construction in progress		6,200,000		6,200,000
Additional construction in progress		12,100,000		12,100,000
Capitalized interest costs during the construction period				100,000
Letter of Credit
Loss Contingencies [Line Items]
Letter of credit issued, classified as long-term restricted cash		1,200,000		$ 1,200,000
South San Francisco California Lease
Loss Contingencies [Line Items]
Lease expiration date				Apr. 30, 2021
Letter of credit expiration date				Dec. 31, 2017
South San Francisco California Lease | Letter of Credit
Loss Contingencies [Line Items]
Letter of credit issued		$ 200,000		$ 200,000
Westlake Village California Lease
Loss Contingencies [Line Items]
Lease expiration date				Apr. 30, 2019
Thousand Oaks California Lease
Loss Contingencies [Line Items]
Lease agreement area of office, lab and cellular therapy manufacturing space | ft²	90,580
Build-to-Suit Lease
Loss Contingencies [Line Items]
Lease initial term	15 years
Contractual obligations	$ 16,400,000
Lease extension term, option one	10 years
Lease extension term, option two	9 years

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Proceeds from issuance of common stock from "at-the-market" facility, net				$ 19,206,000	$ 0
Shares of common stock ,reserved for issuance		11,413,298		11,413,298
Aggregate intrinsic value		$ 4,102,000		$ 4,102,000
Common stock, shares exercised				0	18,947
Option intrinsic value, exercised					$ 200,000
Net tax benefits related to exercised options				$ 0
Granted, Number of shares				1,155,900
Estimated fair value of stock option, vested				$ 10,900,000	10,400,000
Stock-based compensation expense		6,000,000	$ 5,269,000	$ 17,003,000	$ 15,128,000
Weighted average exercise price of options granted				$ 15.99
Non Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted, Number of shares				0	9,000
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average grant date fair value per share				$ 15.07	$ 17.83
Unrecognized stock-based compensation expense		22,800,000		$ 22,800,000
Unrecognized stock-based compensation weighted average recognition period				2 years 9 months 19 days
Aggregate intrinsic value		29,000,000		$ 29,000,000
Restricted stock units, settled				290,534	153,719
Restricted stock units, issued net of tax withholdings				51,592	10,898
Restricted stock units withheld for tax obligations				21,895	4,251
Restricted stock units withheld for tax obligations, value				$ 400,000	$ 75,000
Vested and Unvested Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation weighted average recognition period				2 years 7 months 7 days
Unrecognized stock-based compensation		$ 32,600,000		$ 32,600,000
2014 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock ,reserved for issuance		10,310,669		10,310,669
Aggregate number of awards available for grant to be issued		3,921,737		3,921,737
Outstanding options and RSUs		6,388,932		6,388,932
2014 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock ,reserved for issuance		827,629		827,629
Aggregate number of awards available for grant to be issued		827,630		827,630
Stock-based compensation expense				$ 400,000	$ 300,000
Shares purchased				43,962	0
Outside 2014 EIP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock ,reserved for issuance		275,000		275,000
Granted, Number of shares		145,000	0	275,000	0
Weighted average exercise price of options granted		$ 13.65		$ 13.96
Weighted average grant date fair value of options granted		$ 1,200,000		$ 2,200,000
At The Market Offering | Cowen
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares sold		655,876		1,349,865
Common stock average price		$ 15.55		$ 14.82
Proceeds from issuance of common stock from "at-the-market" facility, net		$ 10,200,000		$ 20,000,000
Net proceeds from sale of common stock after agent commissions and other offering expenses		9,900,000		19,200,000
Common stock value remained available to be sold		$ 55,000,000		$ 55,000,000
At The Market Offering | Cowen | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock aggregate offering price	$ 75,000,000
Percentage of commission to be paid on gross sales proceeds of common stock sold	3.00%

Stockholders' Equity - Summary

Stockholders' Equity - Summary of RSU Activity (Detail) - Unvested RSUs - $ / shares	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Unvested as of December 31, 2016	1,286,262
Shares, Granted	782,413
Shares, Forfeited	(50,063)
Shares, Vested	(282,613)
Shares, Unvested as of September 30, 2017	1,735,999
Shares, Vested and unreleased	17,484
Shares, Outstanding as of September 30, 2017	1,753,483
Weighted Average Grant Date Fair Value, Unvested as of December 31, 2016	$ 16.61
Weighted Average Grant Date Fair Value, Granted	15.07	$ 17.83
Weighted Average Grant Date Fair Value, Forfeited	15.41
Weighted Average Grant Date Fair Value, Vested	12.02
Weighted Average Grant Date Fair Value, Unvested as of September 30, 2017	$ 16.70

Stockholders' Equity - Summar31

Stockholders' Equity - Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2017USD ($)$ / sharesshares	Sep. 30, 2016shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Outstanding, Shares, beginning balance | shares	3,733,847
Granted, Shares | shares	1,155,900
Exercised, Shares | shares	0	(18,947)
Forfeited or expired, Shares | shares	(254,298)
Outstanding, Shares, ending balance | shares	4,635,449
Vested and expected to vest, Shares | shares	4,635,449
Exercisable, Shares | shares	1,887,909
Outstanding, Weighted Average Exercise Price, beginning balance | $ / shares	$ 24.14
Granted, Weighted Average Exercise Price | $ / shares	15.99
Exercised, Weighted Average Exercise Price | $ / shares	0
Forfeited or expired, Weighted Average Exercise price | $ / shares	25.40
Outstanding, Weighted Average Exercise Price, ending balance | $ / shares	22.04
Stock options vested and expected to vest, Weighted Average Exercise Price | $ / shares	22.04
Exercisable, Weighted Average Exercise Price | $ / shares	$ 23.77
Outstanding, Weighted Average Remaining Contractual Term	5 years 3 months 18 days
Stock options vested and expected to vest, Weighted Average Remaining Contractual Term	5 years 3 months 18 days
Exercisable, Weighted Average Remaining Contractual Term	4 years 7 months 6 days
Aggregate intrinsic value | $	$ 4,102
Vested and expected to vest, Aggregate Intrinsic Value | $	4,102
Exercisable, Aggregate Intrinsic Value | $	$ 1,919

Stockholders' Equity - Summar32

Stockholders' Equity - Summary of Estimated Weighted-Average Assumptions (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted	1,155,900
Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	4 years 6 months	4 years 6 months
Expected volatility	69.10%	69.00%
Risk-free interest rate	1.80%	1.30%
Expected dividend yield	0.00%	0.00%
Weighted-average estimated grant date fair value per share	$ 8.88	$ 11.23
Options granted	1,155,900	795,700
Total estimated grant date fair value	$ 10,264,000	$ 8,935,000

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Detail)	Sep. 30, 2017shares
Class Of Stock [Line Items]
Total reserved shares of common stock	11,413,298
2014 Equity Incentive Plan
Class Of Stock [Line Items]
Total reserved shares of common stock	10,310,669
2014 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Total reserved shares of common stock	827,629
Options Issued Outside the 2014 EIP
Class Of Stock [Line Items]
Total reserved shares of common stock	275,000

Stockholders' Equity - Schedu34

Stockholders' Equity - Schedule of Stock-based Compensation Related to All Employee And Non-employee Stock Awards (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 6,000	$ 5,269	$ 17,003	$ 15,128
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	2,136	2,551	6,260	7,231
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 3,864	$ 2,718	$ 10,743	$ 7,897