Atara Biotherapeutics (ATRA) 10-Q 4 May 17 2017 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2017	Apr. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q1
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		29,109,123

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 62,430	$ 47,968
Short-term investments	168,216	207,714
Restricted cash - short-term	194	194
Prepaid expenses and other current assets	4,478	4,677
Total current assets	235,318	260,553
Property and equipment, net	4,400	3,259
Restricted cash - long-term	1,200
Other assets	820	102
Total assets	241,738	263,914
Current liabilities:
Accounts payable	2,204	2,778
Accrued compensation	2,609	3,745
Accrued research and development expenses	2,106	2,408
Other accrued liabilities	886	744
Total current liabilities	7,805	9,675
Long-term liabilities	799	503
Total liabilities	8,604	10,178
Commitments and contingencies (Note 7)
Stockholders’ equity:
Common stock—$0.0001 par value, 500,000 shares authorized as of March 31, 2017 and December 31, 2016; 29,109 and 28,933 shares issued and outstanding as of March 31, 2017 and December 31, 2016, respectively	3	3
Additional paid-in capital	436,096	431,075
Accumulated other comprehensive loss	(152)	(183)
Accumulated deficit	(202,813)	(177,159)
Total stockholders’ equity	233,134	253,736
Total liabilities and stockholders’ equity	$ 241,738	$ 263,914

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 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	29,109	28,933
Common stock, shares outstanding	29,109	28,933

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating expenses:
Research and development	$ 17,541	$ 11,247
General and administrative	8,620	5,814
Total operating expenses	26,161	17,061
Loss from operations	(26,161)	(17,061)
Interest and other income, net	509	503
Loss before provision for income taxes	(25,652)	(16,558)
Less: Provision for income taxes	2	3
Net loss	(25,654)	(16,561)
Other comprehensive loss:
Unrealized gain on available-for-sale securities	31	569
Comprehensive loss	$ (25,623)	$ (15,992)
Net loss per common share:
Basic and diluted net loss per common share	$ (0.88)	$ (0.58)
Weighted-average shares outstanding used to calculate basic and diluted net loss per common share	29,056	28,542

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating activities
Net loss	$ (25,654)	$ (16,561)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	5,347	4,724
Amortization of investment premiums and discounts	301	1,286
Depreciation expense	206	15
Loss on foreign exchange	0	42
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	199	(1,304)
Other assets	(718)	18
Accounts payable	(466)	451
Accrued compensation	(1,136)	(1,287)
Accrued research and development expenses	(302)	(682)
Other accrued liabilities	179	669
Long-term liabilities	10	138
Net cash used in operating activities	(22,034)	(12,491)
Investing activities
Purchases of short-term investments	(51,988)	(130,963)
Maturities of short-term investments	63,760	66,849
Sales of short-term investments	27,456	75,866
Purchases of property and equipment	(1,206)	(891)
Restricted cash	(1,200)	0
Net cash provided by investing activities	36,822	10,861
Financing activities
Taxes paid related to net share settlement of restricted stock units	(326)	(32)
Proceeds from employee stock awards	0	14
Net cash used in financing activities	(326)	(18)
Effect of exchange rates on cash	0	(42)
Increase (decrease) in cash and cash equivalents	14,462	(1,690)
Cash and cash equivalents at beginning of period	47,968	23,746
Cash and cash equivalents at end of period	62,430	22,056
Non-cash investing and financing activities
Issuance of common stock upon vesting of stock awards	0	20
Change in long-term liabilities related to non-vested stock awards	0	(20)
Capitalized lease obligations	286	0
Property and equipment purchases included in liabilities	207	0
Supplemental cash flow disclosure
Cash paid for taxes	$ 2	$ 3

Description of Business

Description of Business	3 Months Ended
	Mar. 31, 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 clinical-stage biopharmaceutical company focused on developing meaningful therapies for patients with severe and life-threatening diseases that have been underserved by scientific innovation. We are focused on developing allogeneic or third-party derived antigen-specific T-cells. T-cells are a type of white blood cell. Cytotoxic T-cells, otherwise known as cytotoxic T lymphocytes, or CTLs, which can mount an immune response against an antigen or antigens in order to combat viral infection or disease. Our cellular therapy platform is designed to provide a healthy immune capability to a patient whose immune system is compromised or is unable to identify the disease targets. 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	3 Months Ended
	Mar. 31, 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 following 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 three month period ended March 31, 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 March 31, 2017 we had an accumulated deficit of $202.8 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 March 31, 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 a newly-leased 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

Net Loss per Common Share

Net Loss per Common Share	3 Months Ended
	Mar. 31, 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 March 31, 2017 2016 Unvested RSAs — 161,779 Unvested RSUs 1,818,315 1,007,542 Vested and unvested options 3,775,661 3,430,482 ESPP share purchase rights 27,765 — Total 5,621,741 4,599,803

Financial Instruments

Financial Instruments	3 Months Ended
	Mar. 31, 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, and 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 March 31, 2017: Input Level Cost Gain Loss Fair Value (in thousands) Money market funds Level 1 $ 46,617 $ — $ — $ 46,617 U.S. Treasury obligations Level 2 54,363 1 (37 ) 54,327 Government agency obligations Level 2 12,343 2 (4 ) 12,341 Corporate debt obligations Level 2 104,168 9 (106 ) 104,071 Commercial paper Level 2 798 — — 798 Asset-backed securities Level 2 12,390 — (17 ) 12,373 Total available-for-sale securities 230,679 12 (164 ) 230,527 Less amounts classified as cash equivalents (62,315 ) — 4 (62,311 ) Amounts classified as short-term securities $ 168,364 $ 12 $ (160 ) $ 168,216 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 securities $ 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 March 31, 2017 As of December 31, 2016 Amortized Estimated Amortized Estimated Cost Fair Value Cost Fair Value (in thousands) (in thousands) Maturing within one year $ 194,903 $ 194,823 $ 198,022 $ 197,956 Maturing in one to five years 35,776 35,704 47,819 47,701 Total available-for-sale securities $ 230,679 $ 230,527 $ 245,841 $ 245,657 As of March 31, 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 loss. 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 March 31, 2017 and December 31, 2016, restricted cash was $1.4 million and $0.2 million, respectively.

Property and Equipment

Property and Equipment	3 Months Ended
	Mar. 31, 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 : March 31, December 31, 2017 2016 (in thousands) Construction in progress $ 2,192 $ 970 Lab equipment 1,631 1,506 Leasehold improvements 580 580 Furniture and fixtures 526 526 Computer equipment and software 66 66 4,995 3,648 Less accumulated depreciation and amortization (595 ) (389 ) Property and equipment, net $ 4,400 $ 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 life of the leasehold improvements or the lease term. Costs for construction in progress relate to expenses capitalized for our planned manufacturing facility in Thousand Oaks, California. Depreciation and amortization expense was $0.2 million and $15,000 for the three months ended March 31, 2017 and 2016, respectively.

License and Collaboration Agree

License and Collaboration Agreements	3 Months Ended
	Mar. 31, 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. 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. 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 March 31, 2017 and December 31, 2016, there were no outstanding obligations for milestones and royalties.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 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 that expires in April 2019. Rent expense for the three months ended March 31, 2017 and 2016 was $0.3 million and $0.3 million, 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 after the end of the construction project when the landlord delivers possession of the property to us. 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 were 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 the accounting owner of these buildings during the construction period, we have recorded approximately $2.2 million as construction in progress through March 31, 2017, representing the costs of the building and improvements incurred and a corresponding long-term financing obligation of $0.3 million. We have also recorded a long-term prepaid asset of $0.8 million for costs of construction paid to our landlord. In addition, we recorded ground lease expense of $37,000 for the three months ended March 31, 2017 in our condensed consolidated statement of operations and comprehensive loss. 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 March 31, 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	3 Months Ended
	Mar. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stockholders' Equity	8. Stockholders’ Equity The following shares of common stock were reserved for future issuance as of March 31, 2017: Total Shares Reserved 2014 Equity Incentive Plan 10,403,584 2014 Employee Stock Purchase Plan 871,592 Total reserved shares of common stock 11,275,176 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 March 31, 2017, a total of 10,403,584 shares of common stock were reserved for issuance under the 2014 Plan, of which 4,784,205 shares were available for future grant and 5,619,379 shares were subject to outstanding options and RSUs. Restricted Stock Units The RSUs granted prior to our October 2014 IPO had a time-based service condition and a liquidity-based performance condition, and vest when both conditions are met. The liquidity-based performance condition was satisfied upon the closing of our IPO. 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 during the three months ended March 31, 2017 and 2016 was $15.09 and $15.78, respectively. As of March 31, 2017, there was $27.1 million of unrecognized stock-based compensation expense related to RSUs that is expected to be recognized over a weighted average period of 3.2 years. The aggregate intrinsic value of the RSUs outstanding as of March 31, 2017 was $37.9 million. 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 744,913 $15.09 Forfeited (16,905 ) $15.49 Vested (195,955 ) $13.34 Unvested as of March 31, 2017 1,818,315 $16.35 Vested and unreleased 25,403 Outstanding as of March 31, 2017 1,843,718 Under our RSU net settlement procedures, we withhold shares at settlement to cover the minimum payroll withholding tax obligations. During the three months ended March 31, 2017, we settled 195,957 RSUs, of which 175,723 RSUs were net settled by withholding 20,234 shares. The value of the RSUs withheld was $0.3 million, based on the closing price of our common stock on the settlement date. During the three months ended March 31, 2016, we settled 52,933 RSUs, of which 50,912 RSUs were net settled by withholding 2,021 shares. The value of the RSUs withheld was $32,000, 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 Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2016 3,733,847 $24.14 Granted 155,100 $14.89 Exercised — $ — Forfeited or expired (113,286 ) $30.79 Outstanding as of March 31, 2017 3,775,661 $23.56 5.5 $6,519 Vested and expected to vest as of March 31, 2017 3,775,661 $23.56 5.5 $6,519 Exercisable as of March 31, 2017 1,392,218 $24.24 5.0 $2,821 Aggregate intrinsic value represents the difference between the closing stock price of our common stock on March 31, 2017 and the exercise price of outstanding, in-the-money options. As of March 31, 2017, there was $29.8 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. No options were exercised during the three months ended March 31, 2017. Options for 1,244 shares of our common stock were exercised during the three months ended March 31, 2016, with an intrinsic value of $10,000. 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: Three months ended March 31, 2017 Three months ended March 31, 2016 Assumptions: Expected term (years) 4.4 4.5 Expected volatility 69.2 % 68.8 % Risk-free interest rate 1.9 % 1.5 % Expected dividend yield 0.0 % 0.0 % Fair Value: Weighted-average estimated grant date fair value per share $ 8.21 $ 11.42 Options granted 155,100 325,900 Total estimated grant date fair value $ 1,273,000 $ 3,722,000 There were no options granted to consultants in the three months ended March 31, 2017 and 2016. The estimated fair value of stock options that vested in the three months ended March 31, 2017 and 2016 was $4.2 million and $2.7 million, respectively. Employee Stock Purchase Plan As of March 31, 2017, there were 871,592 shares available for purchase under the 2014 Employee Stock Purchase Plan (“2014 ESPP”). The Company recorded $0.1 million and no expense related to the 2014 ESPP in the three months ended March 31, 2017 and 2016, respectively. No shares were purchased during the three months ended March 31, 2017 and 2016, respectively. Stock-based Compensation Expense Total stock-based compensation expense related to all employee and non-employee stock awards was as follows: Three 2017 2016 (in thousands) Research and development $ 2,141 $ 2,246 General and administrative 3,206 2,478 Total stock-based compensation expense $ 5,347 $ 4,724

Summary of Significant Accoun14

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 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 following 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 three month period ended March 31, 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 March 31, 2017 we had an accumulated deficit of $202.8 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 March 31, 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 a newly-leased 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

Net Loss per Common Share (Tabl

Net Loss per Common Share (Tables)	3 Months Ended
	Mar. 31, 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 March 31, 2017 2016 Unvested RSAs — 161,779 Unvested RSUs 1,818,315 1,007,542 Vested and unvested options 3,775,661 3,430,482 ESPP share purchase rights 27,765 — Total 5,621,741 4,599,803

Financial Instruments (Tables)

Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 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, and 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 March 31, 2017: Input Level Cost Gain Loss Fair Value (in thousands) Money market funds Level 1 $ 46,617 $ — $ — $ 46,617 U.S. Treasury obligations Level 2 54,363 1 (37 ) 54,327 Government agency obligations Level 2 12,343 2 (4 ) 12,341 Corporate debt obligations Level 2 104,168 9 (106 ) 104,071 Commercial paper Level 2 798 — — 798 Asset-backed securities Level 2 12,390 — (17 ) 12,373 Total available-for-sale securities 230,679 12 (164 ) 230,527 Less amounts classified as cash equivalents (62,315 ) — 4 (62,311 ) Amounts classified as short-term securities $ 168,364 $ 12 $ (160 ) $ 168,216 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 securities $ 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 March 31, 2017 As of December 31, 2016 Amortized Estimated Amortized Estimated Cost Fair Value Cost Fair Value (in thousands) (in thousands) Maturing within one year $ 194,903 $ 194,823 $ 198,022 $ 197,956 Maturing in one to five years 35,776 35,704 47,819 47,701 Total available-for-sale securities $ 230,679 $ 230,527 $ 245,841 $ 245,657

Property and Equipment (Tables)

Property and Equipment (Tables)	3 Months Ended
	Mar. 31, 2017
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consisted of the following as of each period end : March 31, December 31, 2017 2016 (in thousands) Construction in progress $ 2,192 $ 970 Lab equipment 1,631 1,506 Leasehold improvements 580 580 Furniture and fixtures 526 526 Computer equipment and software 66 66 4,995 3,648 Less accumulated depreciation and amortization (595 ) (389 ) Property and equipment, net $ 4,400 $ 3,259

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Common Stock Reserved for Future Issuance	The following shares of common stock were reserved for future issuance as of March 31, 2017: Total Shares Reserved 2014 Equity Incentive Plan 10,403,584 2014 Employee Stock Purchase Plan 871,592 Total reserved shares of common stock 11,275,176
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 744,913 $15.09 Forfeited (16,905 ) $15.49 Vested (195,955 ) $13.34 Unvested as of March 31, 2017 1,818,315 $16.35 Vested and unreleased 25,403 Outstanding as of March 31, 2017 1,843,718
Summary of Stock Option Activity	The following is a summary of stock option activity under our 2014 EIP: Shares Weighted Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2016 3,733,847 $24.14 Granted 155,100 $14.89 Exercised — $ — Forfeited or expired (113,286 ) $30.79 Outstanding as of March 31, 2017 3,775,661 $23.56 5.5 $6,519 Vested and expected to vest as of March 31, 2017 3,775,661 $23.56 5.5 $6,519 Exercisable as of March 31, 2017 1,392,218 $24.24 5.0 $2,821
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 Three months ended March 31, 2017 Three months ended March 31, 2016 Assumptions: Expected term (years) 4.4 4.5 Expected volatility 69.2 % 68.8 % Risk-free interest rate 1.9 % 1.5 % Expected dividend yield 0.0 % 0.0 % Fair Value: Weighted-average estimated grant date fair value per share $ 8.21 $ 11.42 Options granted 155,100 325,900 Total estimated grant date fair value $ 1,273,000 $ 3,722,000
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 2017 2016 (in thousands) Research and development $ 2,141 $ 2,246 General and administrative 3,206 2,478 Total stock-based compensation expense $ 5,347 $ 4,724

Description of Business (Detail

Description of Business (Detail)	3 Months Ended
	Mar. 31, 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	Mar. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Accumulated deficit	$ 202,813	$ 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	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	5,621,741	4,599,803
Unvested RSAs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	0	161,779
Unvested RSUs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	1,818,315	1,007,542
Vested and Unvested Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	3,775,661	3,430,482
ESPP Share Purchase Rights
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	27,765	0

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	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	$ 230,679	$ 245,841
Total Unrealized Gain	12	20
Total Unrealized Loss	(164)	(204)
Total Fair Value	230,527	245,657
Money Market Funds | Level 1
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	46,617	28,816
Total Unrealized Gain	0	0
Total Unrealized Loss	0	0
Total Fair Value	46,617	28,816
U.S. Treasury Obligations | Level 2
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	54,363	65,403
Total Unrealized Gain	1	3
Total Unrealized Loss	(37)	(21)
Total Fair Value	54,327	65,385
Government Agency Obligations | Level 2
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	12,343	23,860
Total Unrealized Gain	2	5
Total Unrealized Loss	(4)	(5)
Total Fair Value	12,341	23,860
Corporate Debt Obligations | Level 2
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	104,168	113,649
Total Unrealized Gain	9	8
Total Unrealized Loss	(106)	(172)
Total Fair Value	104,071	113,485
Commercial Paper | Level 2
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	798	699
Total Unrealized Gain	0	0
Total Unrealized Loss	0	0
Total Fair Value	798	699
Asset-Backed Securities | Level 2
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	12,390	13,414
Total Unrealized Gain	0	4
Total Unrealized Loss	(17)	(6)
Total Fair Value	12,373	13,412
Amounts Classified As Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	62,315	37,944
Total Unrealized Gain	0	0
Total Unrealized Loss	(4)	(1)
Total Fair Value	62,311	37,943
Amounts Classified As Short-Term Securities
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	168,364	207,897
Total Unrealized Gain	12	20
Total Unrealized Loss	(160)	(203)
Total Fair Value	$ 168,216	$ 207,714

Financial Instruments - Amortiz

Financial Instruments - Amortized Cost and Fair Value of Available-for-Sale Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Amortized cost
Maturing within one year, Amortized cost	$ 194,903	$ 198,022
Maturing in one to five years, Amortized cost	35,776	47,819
Total available-for-sale securities, Amortized cost	230,679	245,841
Estimated Fair value
Maturing within one year, Estimated fair value	194,823	197,956
Maturing in one to five years, Estimated fair value	35,704	47,701
Total available-for-sale securities, Estimated fair value	$ 230,527	$ 245,657

Financial Instruments - Additio

Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	Mar. 31, 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	Mar. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 4,995	$ 3,648
Less accumulated depreciation and amortization	(595)	(389)
Property and equipment, net	4,400	3,259
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,192	970
Lab Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,631	1,506
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	580	580
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	526	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 ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Property Plant And Equipment [Line Items]
Depreciation and amortization expense	$ 200,000	$ 15,000
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
	Sep. 30, 2014	Mar. 31, 2017	Sep. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	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	$ 17,541,000		$ 11,247,000
Payments under license agreement		4,500,000
Potential milestone payments payable		33,000,000
Contractual obligations due MSK, Amgen and QIMR		$ 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)	3 Months Ended
	Mar. 31, 2017USD ($)	Mar. 31, 2016USD ($)	Feb. 28, 2017ft²	Dec. 31, 2016USD ($)
Loss Contingencies [Line Items]
Accrued termination charges	$ 0			$ 0
Letter of credit issued	1,400,000			200,000
Rental expenses	300,000	$ 300,000
Letter of credit issued, classified as long-term restricted cash	1,200,000
Long-term prepaid asset for costs of construction paid	800,000
Ground lease expense	37,000
Liabilities related to indemnification agreements	0			$ 0
Building and improvements
Loss Contingencies [Line Items]
Construction in progress	2,200,000
Long-term financing obligations	300,000
Letter of Credit
Loss Contingencies [Line Items]
Letter of credit issued, classified as long-term restricted cash	$ 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
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 - Schedule

Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Detail)	Mar. 31, 2017shares
Class Of Stock [Line Items]
Total reserved shares of common stock	11,275,176
2014 Equity Incentive Plan
Class Of Stock [Line Items]
Total reserved shares of common stock	10,403,584
2014 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Total reserved shares of common stock	871,592

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock ,reserved for issuance	11,275,176
Aggregate intrinsic value	$ 6,519,000
Common stock, shares exercised	0	1,244
Option intrinsic value, exercised		$ 10,000
Net tax benefits related to exercised options	$ 0
Granted, Number of shares	155,100
Estimated fair value of stock option, vested	$ 4,200,000	2,700,000
Stock-based compensation expense	$ 5,347,000	$ 4,724,000
Non Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted, Number of shares	0	0
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average grant date fair value per share	$ 15.09	$ 15.78
Unrecognized stock-based compensation expense	$ 27,100,000
Unrecognized stock-based compensation weighted average recognition period	3 years 2 months 12 days
Aggregate intrinsic value	$ 37,900,000
Restricted stock units, settled	195,957	52,933
Restricted stock units, issued net of tax withholdings	175,723	50,912
Restricted stock units withheld for tax obligations	20,234	2,021
Restricted stock units withheld for tax obligations, value	$ 300,000	$ 32,000
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 6 days
Unrecognized stock-based compensation	$ 29,800,000
2014 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock ,reserved for issuance	10,403,584
Aggregate number of awards available for grant to be issued	4,784,205
Outstanding options and RSUs	5,619,379
2014 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock ,reserved for issuance	871,592
Aggregate number of awards available for grant to be issued	871,592
Stock-based compensation expense	$ 100,000	$ 0
Shares purchased	0	0

Stockholders' Equity - Summary

Stockholders' Equity - Summary of RSU Activity (Detail) - Unvested RSUs - $ / shares	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested as of December 31, 2016	1,286,262
Granted	744,913
Forfeited	(16,905)
Vested	(195,955)
Unvested as of March 31, 2017	1,818,315
Vested and unreleased	25,403
Outstanding as of March 31, 2017	1,843,718
Unvested as of December 31, 2016	$ 16.61
Granted	15.09	$ 15.78
Forfeited	15.49
Vested	13.34
Unvested as of March 31, 2017	$ 16.35

Stockholders' Equity - Summar32

Stockholders' Equity - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Outstanding, Shares, beginning balance	3,733,847
Granted, Shares	155,100
Exercised, Shares	0	(1,244)
Forfeited or expired, Shares	(113,286)
Outstanding, Shares, ending balance	3,775,661
Vested and expected to vest, Shares	3,775,661
Exercisable, Shares	1,392,218
Outstanding, Weighted Average Exercise Price, beginning balance	$ 24.14
Granted, Weighted Average Exercise Price	14.89
Exercised, Weighted Average Exercise Price	0
Forfeited or expired, Weighted Average Exercise price	30.79
Outstanding, Weighted Average Exercise Price, ending balance	23.56
Stock options vested and expected to vest, Weighted Average Exercise Price	23.56
Exercisable, Weighted Average Exercise Price	$ 24.24
Outstanding, Weighted Average Remaining Contractual Term	5 years 6 months
Stock options vested and expected to vest, Weighted Average Remaining Contractual Term	5 years 6 months
Exercisable, Weighted Average Remaining Contractual Term	5 years
Aggregate intrinsic value	$ 6,519
Vested and expected to vest, Aggregate Intrinsic Value	6,519
Exercisable, Aggregate Intrinsic Value	$ 2,821

Stockholders' Equity - Summar33

Stockholders' Equity - Summary of Estimated Weighted-Average Assumptions (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted	155,100
Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	4 years 4 months 24 days	4 years 6 months
Expected volatility	69.20%	68.80%
Risk-free interest rate	1.90%	1.50%
Expected dividend yield	0.00%	0.00%
Weighted-average estimated grant date fair value per share	$ 8.21	$ 11.42
Options granted	155,100	325,900
Total estimated grant date fair value	$ 1,273,000	$ 3,722,000

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
	Mar. 31, 2017	Mar. 31, 2016
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 5,347	$ 4,724
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	2,141	2,246
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 3,206	$ 2,478