Five Prime Therapeutics (FPRX) 10-Q 8 Aug 17 2017 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2017	Aug. 01, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q2
Trading Symbol	FPRX
Entity Registrant Name	FIVE PRIME THERAPEUTICS INC
Entity Central Index Key	1,175,505
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		28,902,102

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 59,709	$ 7,653
Marketable securities	291,009	414,095
Receivables from collaborative partners	3,832	3,959
Income tax receivable		4,670
Prepaid and other current assets	8,754	9,748
Total current assets	363,304	440,125
Restricted cash	1,543	1,543
Property and equipment, net	15,227	6,207
Other long-term assets	37	406
Total assets	380,111	448,281
Current liabilities:
Accounts payable	1,321	334
Accrued personnel-related expenses	5,377	7,957
Other accrued liabilities	15,113	15,435
Deferred revenue, current portion	13,325	14,150
Deferred rent, current portion	433	865
Total current liabilities	35,569	38,741
Deferred revenue, long-term portion	12,033	17,856
Deferred rent, long-term portion	1,812
Other long-term liabilities	7,423	109
Commitments
Stockholders' equity:
Common stock, $0.001 par value; 100,000,000 shares authorized, 28,804,182 issued and 27,985,692 outstanding at June 30, 2017. 28,550,006 issued and 27,509,077 outstanding at December 31, 2016	28	27
Additional paid-in capital	406,664	396,635
Accumulated other comprehensive loss	(304)	(39)
Accumulated deficit	(83,114)	(5,048)
Total stockholders' equity	323,274	391,575
Total liabilities and stockholders' equity	$ 380,111	$ 448,281

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	28,804,182	28,550,006
Common stock, shares outstanding	27,985,692	27,509,077

Condensed Statements of Operati

Condensed Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Collaboration revenue	$ 7,822	$ 9,229	$ 17,957	$ 15,749
Operating expenses:
Research and development	41,744	22,177	75,504	41,033
General and administrative	9,363	8,106	19,849	16,163
Total operating expenses	51,107	30,283	95,353	57,196
Loss from operations	(43,285)	(21,054)	(77,396)	(41,447)
Interest and other income, net	702	646	1,370	1,182
Loss before income tax	(42,583)	(20,408)	(76,026)	(40,265)
Income tax (provision) benefit	(1,703)	7,271	(1,703)	14,088
Net loss	$ (44,286)	$ (13,137)	$ (77,729)	$ (26,177)
Basic and diluted net loss per common share	$ (1.58)	$ (0.49)	$ (2.79)	$ (0.98)
Weighted-average shares used to compute basic and diluted net loss per common share	27,946	26,924	27,813	26,619

Condensed Statements of Compreh

Condensed Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (44,286)	$ (13,137)	$ (77,729)	$ (26,177)
Other comprehensive income (loss):
Net unrealized gain (loss) on marketable securities, net of tax	(60)	109	(265)	293
Comprehensive loss	$ (44,346)	$ (13,028)	$ (77,994)	$ (25,884)

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating activities
Net loss	$ (77,729)	$ (26,177)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,112	782
Stock-based compensation expense	19,648	14,527
Excess tax benefits from employee equity incentive plans		(2,533)
Deferred income taxes		3,451
Amortization of premiums and discounts on marketable securities	1,223	2,346
Loss (gain) on disposal of property and equipment	2	(9)
Changes in operating assets and liabilities:
Receivables from collaborative partners	127	655
Income tax receivable	4,670	(1,504)
Prepaid, other current assets, and other long-term assets	1,363	770
Accounts payable	987	(1,240)
Accrued personnel-related expenses	(2,580)	(2,863)
Deferred revenue	(6,648)	(8,618)
Deferred rent	1,185	(383)
Income tax payable		(30,580)
Other accrued liabilities and other long-term liabilities	(377)	2,210
Net cash used in operating activities	(57,017)	(49,166)
Investing activities
Purchases of marketable securities	(220,652)	(339,880)
Maturities of marketable securities	342,250	274,250
Purchases of property and equipment	(2,581)	(1,868)
Proceeds from disposal of property and equipment	12
Net cash provided by (used in) investing activities	119,029	(67,498)
Financing activities
Proceeds from issuance of common stock under equity incentive plans	2,230	5,916
Repurchase of shares to satisfy tax withholding obligations	(12,186)	(3,602)
Excess tax benefits from employee equity incentive plans		2,533
Net cash (used in) provided by financing activities	(9,956)	4,847
Net increase (decrease) in cash and cash equivalents	52,056	(111,817)
Cash and cash equivalents at beginning of period	7,653	149,971
Cash and cash equivalents at end of period	59,709	38,154
Supplemental cash flow information
Cash paid for income taxes		$ 14,701
Non-cash investing activities
Unpaid property and equipment purchases included in accrued liabilities	403
Tenant improvements provided by the landlord	$ 8,291

Description of Business

Description of Business	6 Months Ended
	Jun. 30, 2017
Accounting Policies [Abstract]
Description of Business	1. Description of Business Five Prime Therapeutics, Inc. (we, us, our, or the Company) is a clinical-stage biotechnology company focused on discovering and developing innovative protein therapeutics. We were incorporated in December 2001 in Delaware. Our operations are based in South San Francisco, California and we operate in one segment. Unaudited Interim Financial Information The accompanying financial information as of June 30, 2017 is unaudited. The condensed financial statements included in this report reflect all adjustments (consisting only of normal recurring adjustments) that our management considers necessary for the fair statement of the results of operations for the interim periods covered and of the financial condition of the Company at the date of the interim balance sheet. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles, or GAAP, for interim financial information. Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. The results for interim periods are not necessarily indicative of the results for the entire year or any other interim period. The accompanying condensed financial statements and related financial information should be read in conjunction with the audited financial statements and the related notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2016 filed with the U.S. Securities and Exchange Commission.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions about future events that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ materially from those estimates. Fair Value of Financial Instruments We determine the fair value of financial and nonfinancial assets and liabilities using the fair value hierarchy, which describes three levels of inputs that may be used to measure fair value, as follows: Level 1 —Quoted prices in active markets for identical assets or liabilities; Level 2 —Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and Level 3 —Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. We determine the fair value of Level 1 assets using quoted prices in active markets for identical assets. We review trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, which are obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data. There were no transfers between Level 1 and Level 2 securities in the periods presented. In certain cases where there is limited activity or less transparency around inputs to valuation, we classify securities as Level 3 within the valuation hierarchy. We do not have any assets or liabilities measured using Level 3 inputs as of June 30, 2017. The following table summarizes our financial instruments that were measured at fair value on a recurring basis by level of input within the fair value hierarchy defined above (in thousands): June 30, 2017 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 44,600 $ 44,600 $ — $ — U.S. Treasury securities 291,009 291,009 — — Certificate of deposit 1,543 — 1,543 — Total cash equivalents and marketable securities $ 337,152 $ 335,609 $ 1,543 $ — December 31, 2016 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 432 $ 432 $ — $ — U.S. Treasury securities 414,095 414,095 — — Certificate of deposit 1,543 — 1,543 — Total cash equivalents and marketable securities $ 416,070 $ 414,527 $ 1,543 $ — Net Loss Per Share of Common Stock We compute basic net loss per common share by dividing net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period. We excluded the following securities from the calculation of diluted net loss per share as the effect would have been antidilutive (in thousands): Three Months Ended Six Months Ended June 30, June 30, 2017 2016 2017 2016 Options to purchase common stock 3,879 2,561 3,796 2,739 Restricted stock awards (RSAs) 834 1,319 940 1,412 4,713 3,880 4,736 4,151 Accounting Pronouncements Adopted in 2017 In March 2016, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, 2016-09, Improvements to Employee Share-Based Payment Accounting Accounting Pronouncements Not Yet Adopted In May 2014, FASB issued ASU 2014-09, Revenue from Contracts with Customers: Topic 606 In March, April, May and December 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers: Principal versus Agent Considerations , ASU 2016-10, Revenue from Contracts with Customers: Identifying Performance Obligations and Licensing , ASU 2016-12, Revenue from Contracts with Customers: Narrow-Scope Improvements and Practical Expedients to provide supplemental adoption guidance and clarification to ASU 2014-09 and ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers , respectively. The effective date for these new standards is the same as the effective date and transition requirements for ASU 2014-09. We expect to adopt ASU 2014-09 in the first quarter of 2018 using the modified retrospective method. Our adoption of ASU 2014-09 may have a material effect on our financial statements. To date, we have derived our revenues from license and collaboration agreements. The consideration we are eligible to receive under these agreements includes upfront payments, research and development funding, milestone payments and royalties. Each license and collaboration agreement is unique and will need to be assessed separately under the five-step process set forth in under the new standard. We are currently assessing our active license and collaboration agreements. We expect that our evaluation of the accounting for license and collaboration agreements under the new revenue standard could identify material changes from the current accounting treatment. ASU 2014-09 differs from the current accounting standard in many respects, such as in the accounting for variable consideration, including milestone payments. Under our current accounting policy, we recognize milestone revenue using the milestone method specified in ASC 605-28, which generally results in the recognition of the milestone payment as revenue in the period that the milestone is achieved. However, under the new accounting standard, it is possible to start to recognize milestone revenue before the milestone is achieved, subject to management’s assessment of whether it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. In addition, the current accounting standards include a presumption that revenue from up-front non-refundable fees would be recognized ratably over the performance period, unless another attribution method was determined to more closely approximate the delivery of the goods or services to the customer. The new accounting standard does not have a presumption that entities would default to a ratable attribution approach and will require entities to determine an appropriate attribution method using either output or input methods. As such, the amount and timing of revenue recognition for our license and collaboration agreements may change under the new revenue standard. In February 2016, FASB issued ASU 2016-02, Leases all annual and interim reporting periods thereafter. E In May 2017, FASB issued ASU 2017-09, Compensation-Stock Compensation (Topic 718) – Scope of Modification Accounting

Cash Equivalents and Marketable

Cash Equivalents and Marketable Securities	6 Months Ended
	Jun. 30, 2017
Cash And Cash Equivalents [Abstract]
Cash Equivalents and Marketable Securities	3. Cash Equivalents and Marketable Securities The following table summarizes our cash equivalents and marketable securities (in thousands): June 30, 2017 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 44,600 $ — $ — $ 44,600 U.S. Treasury securities 291,313 — (304 ) 291,009 335,913 — (304 ) 335,609 Less: cash equivalents (44,600 ) — — (44,600 ) Total marketable securities $ 291,313 $ — $ (304 ) $ 291,009 December 31, 2016 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 432 $ — $ — $ 432 U.S. Treasury securities 414,134 54 (93 ) 414,095 414,566 54 (93 ) 414,527 Less: cash equivalents (432 ) — — (432 ) Total marketable securities $ 414,134 $ 54 $ (93 ) $ 414,095 As of June 30, 2017, the amortized cost and estimated fair value of our available-for-sale securities by contractual maturity are shown below (in thousands): Amortized Estimated Cost Fair Value Debt securities maturing: In one year or less $ 286,339 $ 286,042 In one to two years 4,974 4,967 Total marketable securities $ 291,313 $ 291,009 We determined that the gross unrealized losses on our marketable securities as of June 30, 2017 were temporary in nature. We currently do not intend to sell these securities prior to maturity and do not consider these investments to be other-than-temporarily impaired at June 30, 2017. There were no sales of available-for-sale securities in any of the periods presented.

Equity Incentive Plans

Equity Incentive Plans	6 Months Ended
	Jun. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity Incentive Plans	4. Equity Incentive Plans The following table summarizes option activity under our equity incentive plans and related information: Options Outstanding Weighted Weighted Average Average Remaining Number of Exercise Price Contractual Shares Per Share Term (years) Balance at December 31, 2016 3,454,339 $ 26.80 Options granted 699,050 $ 41.91 Options exercised (115,944 ) $ 12.37 Options forfeited (160,002 ) $ 37.87 Options expired (552 ) $ 43.93 Balance at June 30, 2017 3,876,891 $ 29.50 Options exercisable as of June 30, 2017 1,748,719 $ 19.87 6.00 We have granted RSAs to certain of our employees, some of which are subject to performance conditions. RSAs are share awards that entitle the holder to receive freely tradable shares of our common stock upon vesting and are not forfeitable once fully vested. We based the fair value of RSAs on the closing sale price of our common stock on the grant date. For awards subject to performance conditions, we recognize stock-based compensation expense using the accelerated attribution recognition method when it is probable that the performance condition will be achieved. The following table summarizes RSA activity under our 2013 Omnibus Incentive Plan and related information: RSAs Outstanding Weighted-Average Number Grant-Date of Shares Fair Value Unvested balance at December 31, 2016 1,040,929 $ 28.84 RSAs granted 452,555 $ 43.96 RSAs vested (602,467 ) $ 20.24 RSAs forfeited (72,527 ) $ 42.50 Unvested balance at June 30, 2017 818,490 $ 42.32 As of June 30, 2017, there were 1,564,142 shares of common stock available for future issuance under our 2013 Omnibus Incentive Plan. Stock-Based Compensation Total stock-based compensation expense recognized was as follows (in thousands): Three Months Ended Six Months Ended June 30, June 30, 2017 2016 2017 2016 Research and development $ 5,930 $ 3,868 $ 11,216 $ 8,143 General and administrative 3,831 3,258 8,432 6,384 Total $ 9,761 $ 7,126 $ 19,648 $ 14,527 We estimated the fair value of stock options using the Black-Scholes option-pricing model based on the date of grant of such stock option with the following assumptions: Three Months Ended Six Months Ended June 30, June 30, 2017 2016 2017 2016 Expected term (years) 5.5-6.3 5.5-6.3 5.5-6.3 5.5-6.3 Expected volatility 66% 72% 66-68% 72-74% Risk-free interest rate 1.9% 1.4% 1.9-2.1 1.4-1.5% Expected dividend yield 0% 0% 0% 0% As of June 30, 2017, we had $46.4 million of total unrecognized compensation expense related to unvested employee and director stock options that we expect to recognize over a weighted-average period of 2.8 years. Additionally, we had $26.2 million of total unrecognized compensation expense related to employee and director RSAs that we expect to recognize over a weighted-average period of 2.2 years.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	5. Income Taxes We recorded a provision for income taxes of $1.7 million for the three and six months ended June 30, 2017 based on our ongoing discussions with the Internal Revenue Service as to our tentative net operating loss carryback refund claim filed in March 2017. We realized an income tax benefit of $7.3 million and $14.1 million for the three and six months ended June 30, 2016, respectively. This income tax benefit represented our ability to recover taxes accrued in 2015 based on existing tax law that allowed us to carryback our 2016 tax losses and/or credits to recover prior taxes. The income tax benefit was based on the annual effective tax rate method and considered our forecasted 2016 pre-tax losses reduced by non-deductible stock based compensation expenses and other immaterial non-deductible permanent items. In addition, as a result of the forecasted loss, the income tax benefit was decreased by a valuation allowance recorded against certain deferred tax assets due to the uncertainty surrounding the realization of such assets in the future. After the carryback of our full year 2016 net operating losses to 2015, we maximized our ability to obtain a refund of prior income taxes paid.

Summary of Significant Accoun12

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2017
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions about future events that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ materially from those estimates.
Fair Value of Financial Instruments	Fair Value of Financial Instruments We determine the fair value of financial and nonfinancial assets and liabilities using the fair value hierarchy, which describes three levels of inputs that may be used to measure fair value, as follows: Level 1 —Quoted prices in active markets for identical assets or liabilities; Level 2 —Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and Level 3 —Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. We determine the fair value of Level 1 assets using quoted prices in active markets for identical assets. We review trading activity and pricing for Level 2 investments as of each measurement date. Level 2 inputs, which are obtained from various third-party data providers, represent quoted prices for similar assets in active markets and were derived from observable market data, or, if not directly observable, were derived from or corroborated by other observable market data. There were no transfers between Level 1 and Level 2 securities in the periods presented. In certain cases where there is limited activity or less transparency around inputs to valuation, we classify securities as Level 3 within the valuation hierarchy. We do not have any assets or liabilities measured using Level 3 inputs as of June 30, 2017. The following table summarizes our financial instruments that were measured at fair value on a recurring basis by level of input within the fair value hierarchy defined above (in thousands): June 30, 2017 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 44,600 $ 44,600 $ — $ — U.S. Treasury securities 291,009 291,009 — — Certificate of deposit 1,543 — 1,543 — Total cash equivalents and marketable securities $ 337,152 $ 335,609 $ 1,543 $ — December 31, 2016 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 432 $ 432 $ — $ — U.S. Treasury securities 414,095 414,095 — — Certificate of deposit 1,543 — 1,543 — Total cash equivalents and marketable securities $ 416,070 $ 414,527 $ 1,543 $ —
Net Loss Per Share of Common Stock	Net Loss Per Share of Common Stock We compute basic net loss per common share by dividing net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period. We excluded the following securities from the calculation of diluted net loss per share as the effect would have been antidilutive (in thousands): Three Months Ended Six Months Ended June 30, June 30, 2017 2016 2017 2016 Options to purchase common stock 3,879 2,561 3,796 2,739 Restricted stock awards (RSAs) 834 1,319 940 1,412 4,713 3,880 4,736 4,151
Accounting Pronouncements Adopted in 2017	Accounting Pronouncements Adopted in 2017 In March 2016, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, 2016-09, Improvements to Employee Share-Based Payment Accounting
Accounting Pronouncements Not Yet Adopted	Accounting Pronouncements Not Yet Adopted In May 2014, FASB issued ASU 2014-09, Revenue from Contracts with Customers: Topic 606 In March, April, May and December 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers: Principal versus Agent Considerations , ASU 2016-10, Revenue from Contracts with Customers: Identifying Performance Obligations and Licensing , ASU 2016-12, Revenue from Contracts with Customers: Narrow-Scope Improvements and Practical Expedients to provide supplemental adoption guidance and clarification to ASU 2014-09 and ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers , respectively. The effective date for these new standards is the same as the effective date and transition requirements for ASU 2014-09. We expect to adopt ASU 2014-09 in the first quarter of 2018 using the modified retrospective method. Our adoption of ASU 2014-09 may have a material effect on our financial statements. To date, we have derived our revenues from license and collaboration agreements. The consideration we are eligible to receive under these agreements includes upfront payments, research and development funding, milestone payments and royalties. Each license and collaboration agreement is unique and will need to be assessed separately under the five-step process set forth in under the new standard. We are currently assessing our active license and collaboration agreements. We expect that our evaluation of the accounting for license and collaboration agreements under the new revenue standard could identify material changes from the current accounting treatment. ASU 2014-09 differs from the current accounting standard in many respects, such as in the accounting for variable consideration, including milestone payments. Under our current accounting policy, we recognize milestone revenue using the milestone method specified in ASC 605-28, which generally results in the recognition of the milestone payment as revenue in the period that the milestone is achieved. However, under the new accounting standard, it is possible to start to recognize milestone revenue before the milestone is achieved, subject to management’s assessment of whether it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. In addition, the current accounting standards include a presumption that revenue from up-front non-refundable fees would be recognized ratably over the performance period, unless another attribution method was determined to more closely approximate the delivery of the goods or services to the customer. The new accounting standard does not have a presumption that entities would default to a ratable attribution approach and will require entities to determine an appropriate attribution method using either output or input methods. As such, the amount and timing of revenue recognition for our license and collaboration agreements may change under the new revenue standard. In February 2016, FASB issued ASU 2016-02, Leases all annual and interim reporting periods thereafter. E In May 2017, FASB issued ASU 2017-09, Compensation-Stock Compensation (Topic 718) – Scope of Modification Accounting

Summary of Significant Accoun13

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2017
Accounting Policies [Abstract]
Summary of Financial Instruments Measured at Fair Value	The following table summarizes our financial instruments that were measured at fair value on a recurring basis by level of input within the fair value hierarchy defined above (in thousands): June 30, 2017 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 44,600 $ 44,600 $ — $ — U.S. Treasury securities 291,009 291,009 — — Certificate of deposit 1,543 — 1,543 — Total cash equivalents and marketable securities $ 337,152 $ 335,609 $ 1,543 $ — December 31, 2016 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 432 $ 432 $ — $ — U.S. Treasury securities 414,095 414,095 — — Certificate of deposit 1,543 — 1,543 — Total cash equivalents and marketable securities $ 416,070 $ 414,527 $ 1,543 $ —
Securities Excluded from Calculation of Diluted Net Loss Per Share	We excluded the following securities from the calculation of diluted net loss per share as the effect would have been antidilutive (in thousands): Three Months Ended Six Months Ended June 30, June 30, 2017 2016 2017 2016 Options to purchase common stock 3,879 2,561 3,796 2,739 Restricted stock awards (RSAs) 834 1,319 940 1,412 4,713 3,880 4,736 4,151

Cash Equivalents and Marketab14

Cash Equivalents and Marketable Securities (Tables)	6 Months Ended
	Jun. 30, 2017
Cash And Cash Equivalents [Abstract]
Summary of Cash Equivalents and Marketable Securities	The following table summarizes our cash equivalents and marketable securities (in thousands): June 30, 2017 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 44,600 $ — $ — $ 44,600 U.S. Treasury securities 291,313 — (304 ) 291,009 335,913 — (304 ) 335,609 Less: cash equivalents (44,600 ) — — (44,600 ) Total marketable securities $ 291,313 $ — $ (304 ) $ 291,009 December 31, 2016 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 432 $ — $ — $ 432 U.S. Treasury securities 414,134 54 (93 ) 414,095 414,566 54 (93 ) 414,527 Less: cash equivalents (432 ) — — (432 ) Total marketable securities $ 414,134 $ 54 $ (93 ) $ 414,095
Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity	As of June 30, 2017, the amortized cost and estimated fair value of our available-for-sale securities by contractual maturity are shown below (in thousands): Amortized Estimated Cost Fair Value Debt securities maturing: In one year or less $ 286,339 $ 286,042 In one to two years 4,974 4,967 Total marketable securities $ 291,313 $ 291,009

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	6 Months Ended
	Jun. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Option Activity under Equity Incentive Plans and Related Information	The following table summarizes option activity under our equity incentive plans and related information: Options Outstanding Weighted Weighted Average Average Remaining Number of Exercise Price Contractual Shares Per Share Term (years) Balance at December 31, 2016 3,454,339 $ 26.80 Options granted 699,050 $ 41.91 Options exercised (115,944 ) $ 12.37 Options forfeited (160,002 ) $ 37.87 Options expired (552 ) $ 43.93 Balance at June 30, 2017 3,876,891 $ 29.50 Options exercisable as of June 30, 2017 1,748,719 $ 19.87 6.00
Schedule of Restricted Stock Award Activity under 2013 Omnibus Incentive Plan and Related Information	The following table summarizes RSA activity under our 2013 Omnibus Incentive Plan and related information: RSAs Outstanding Weighted-Average Number Grant-Date of Shares Fair Value Unvested balance at December 31, 2016 1,040,929 $ 28.84 RSAs granted 452,555 $ 43.96 RSAs vested (602,467 ) $ 20.24 RSAs forfeited (72,527 ) $ 42.50 Unvested balance at June 30, 2017 818,490 $ 42.32
Schedule of Stock-Based Compensation Expenses Recognized	Total stock-based compensation expense recognized was as follows (in thousands) Three Months Ended Six Months Ended June 30, June 30, 2017 2016 2017 2016 Research and development $ 5,930 $ 3,868 $ 11,216 $ 8,143 General and administrative 3,831 3,258 8,432 6,384 Total $ 9,761 $ 7,126 $ 19,648 $ 14,527
Schedule of Stock Options Weighted-Average Assumptions	We estimated the fair value of stock options using the Black-Scholes option-pricing model based on the date of grant of such stock option with the following assumptions: Three Months Ended Six Months Ended June 30, June 30, 2017 2016 2017 2016 Expected term (years) 5.5-6.3 5.5-6.3 5.5-6.3 5.5-6.3 Expected volatility 66% 72% 66-68% 72-74% Risk-free interest rate 1.9% 1.4% 1.9-2.1 1.4-1.5% Expected dividend yield 0% 0% 0% 0%

Description of Business - Addit

Description of Business - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2017Segment
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of operating segment	1

Summary of Significant Accoun17

Summary of Significant Accounting Policies - Summary of Financial Instruments Measured at Fair Value (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Assets
Total cash equivalents and marketable securities	$ 337,152	$ 416,070
Money market funds [Member]
Assets
Cash equivalents	44,600	432
Certificate of deposit [Member]
Assets
Cash equivalents	1,543	1,543
Level 1 [Member]
Assets
Total cash equivalents and marketable securities	335,609	414,527
Level 1 [Member] | Money market funds [Member]
Assets
Cash equivalents	44,600	432
Level 2 [Member]
Assets
Total cash equivalents and marketable securities	1,543	1,543
Level 2 [Member] | Certificate of deposit [Member]
Assets
Cash equivalents	1,543	1,543
U.S. Treasury securities [Member]
Assets
U.S. Treasury securities	291,009	414,095
U.S. Treasury securities [Member] | Level 1 [Member]
Assets
U.S. Treasury securities	$ 291,009	$ 414,095

Summary of Significant Accoun18

Summary of Significant Accounting Policies - Securities Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net loss per share	4,713	3,880	4,736	4,151
Options to purchase common stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net loss per share	3,879	2,561	3,796	2,739
Restricted stock awards (RSAs) [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net loss per share	834	1,319	940	1,412

Summary of Significant Accoun19

Summary of Significant Accounting Policies - Additional Information (Detail) - ASU 2016-09 [Member]	Jan. 01, 2017USD ($)
Summary Of Significant Accounting Policies [Line Items]
Decrease to retained earnings	$ 337,000
Increase in deferred tax assets which is fully offset by valuation allowance	$ 3,100,000

Cash Equivalents and Marketab20

Cash Equivalents and Marketable Securities - Summary of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	$ 291,313	$ 414,134
Unrealized Gains		54
Unrealized Losses	(304)	(93)
Estimated Fair Value	291,009	414,095
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	44,600	432
Estimated Fair Value	44,600	432
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	291,313	414,134
Unrealized Gains		54
Unrealized Losses	(304)	(93)
Estimated Fair Value	291,009	414,095
Marketable securities including cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	335,913	414,566
Unrealized Gains		54
Unrealized Losses	(304)	(93)
Estimated Fair Value	335,609	414,527
Cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	(44,600)	(432)
Estimated Fair Value	$ (44,600)	$ (432)

Cash Equivalents and Marketab21

Cash Equivalents and Marketable Securities - Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	$ 291,313	$ 414,134
Total marketable securities, Estimated Fair Value	291,009	414,095
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, In one year or less	286,339
Amortized Cost, In one to two years	4,974
Amortized Cost Basis	291,313	414,134
Estimated Fair Value, In one year or less	286,042
Estimated Fair Value, In one to two years	4,967
Total marketable securities, Estimated Fair Value	$ 291,009	$ 414,095

Cash Equivalents and Marketab22

Cash Equivalents and Marketable Securities - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2017USD ($)
Investments Debt And Equity Securities [Abstract]
Sales of available-for-sale securities	$ 0

Equity Incentive Plans - Schedu

Equity Incentive Plans - Schedule of Option Activity under Equity Incentive Plans and Related Information (Detail)	6 Months Ended
	Jun. 30, 2017$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning balance | shares	3,454,339
Number of Shares, Options granted | shares	699,050
Number of Shares, Options exercised | shares	(115,944)
Number of Shares, Options forfeited | shares	(160,002)
Number of Shares, Options expired | shares	(552)
Number of Shares, Ending balance | shares	3,876,891
Number of Shares, Options exercisable | shares	1,748,719
Weighted-Average Exercise Price Per Share, Options beginning balance | $ / shares	$ 26.80
Weighted-Average Exercise Price Per Share, Options granted | $ / shares	41.91
Weighted-Average Exercise Price Per Share, Options exercised | $ / shares	12.37
Weighted-Average Exercise Price Per Share, Options forfeited | $ / shares	37.87
Weighted-Average Exercise Price Per Share, Options expired | $ / shares	43.93
Weighted-Average Exercise Price Per Share, Options ending balance | $ / shares	29.50
Weighted-Average Exercise Price Per Share, Options exercisable | $ / shares	$ 19.87
Weighted Average Remaining Contractual Term, Options exercisable	6 years

Equity Incentive Plans - Sche24

Equity Incentive Plans - Schedule of Restricted Stock Award Activity under 2013 Omnibus Incentive Plan and Related Information (Detail) - Restricted Stock Awards [Member]	6 Months Ended
	Jun. 30, 2017$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Unvested, beginning balance | shares	1,040,929
Number of Shares, Granted | shares	452,555
Number of Shares, Vested | shares	(602,467)
Number of Shares, Forfeited | shares	(72,527)
Number of Shares, Unvested, Ending balance | shares	818,490
Weighted-Average Grant-Date Fair Value, Unvested, Beginning balance | $ / shares	$ 28.84
Weighted-Average Grant-Date Fair Value, Granted | $ / shares	43.96
Weighted-Average Grant-Date Fair Value, Vested | $ / shares	20.24
Weighted-Average Grant-Date Fair Value, Forfeited | $ / shares	42.50
Weighted-Average Grant-Date Fair Value, Unvested, Ending balance | $ / shares	$ 42.32

Equity Incentive Plans - Additi

Equity Incentive Plans - Additional Information (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2017USD ($)shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized compensation expense related to unvested employee and director stock options	$ 46.4
Unrecognized compensation expense expected to recognize, weighted-average period	2 years 9 months 18 days
Restricted Stock Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense expected to recognize, weighted-average period	2 years 2 months 12 days
Total unrecognized compensation expense related to employee and director RSAs	$ 26.2
2013 Omnibus Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock reserved for future issuance | shares	1,564,142

Equity Incentive Plans - Sche26

Equity Incentive Plans - Schedule of Stock-Based Compensation Expenses Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	$ 9,761	$ 7,126	$ 19,648	$ 14,527
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	5,930	3,868	11,216	8,143
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	$ 3,831	$ 3,258	$ 8,432	$ 6,384

Equity Incentive Plans - Sche27

Equity Incentive Plans - Schedule of Stock Options Assumptions (Detail) - Options [Member]	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility	66.00%	72.00%
Risk-free interest rate	1.90%	1.40%
Risk-free interest rate, minimum			1.90%	1.40%
Risk-free interest rate, maximum			2.10%	1.50%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	5 years 6 months	5 years 6 months	5 years 6 months	5 years 6 months
Expected volatility			66.00%	72.00%
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years 3 months 18 days	6 years 3 months 18 days	6 years 3 months 18 days	6 years 3 months 18 days
Expected volatility			68.00%	74.00%

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Tax Disclosure [Abstract]
Income tax provision (benefit)	$ 1,703	$ (7,271)	$ 1,703	$ (14,088)