Five Prime Therapeutics (FPRX) 10-Q 6 May 16 2016 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2016	Apr. 29, 2016
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q1
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	Accelerated Filer
Entity Common Stock, Shares Outstanding		28,200,759

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 133,011	$ 149,971
Marketable securities	348,975	367,495
Receivables from collaborative partners	1,760	4,054
Income tax receivable	822
Prepaid and other current assets	6,009	6,761
Total current assets	490,577	528,281
Property and equipment, net	4,987	4,539
Deferred tax asset	13,302	15,071
Other long-term assets	390	394
Total assets	509,256	548,285
Current liabilities:
Accounts payable	1,020	1,894
Accrued personnel-related expenses	3,848	6,878
Other accrued liabilities	4,340	5,882
Deferred revenue, current portion	16,214	17,509
Deferred rent, current portion	792	768
Income tax payable, current portion	23,573	46,437
Total current liabilities	49,787	79,368
Deferred revenue, long-term portion	27,915	31,268
Deferred rent, long-term portion	649	865
Income tax payable, long-term portion	2,547	3,283
Other long-term liabilities	$ 221	$ 295
Commitments
Stockholders' equity:
Common stock	$ 27	$ 26
Additional paid-in capital	380,391	372,605
Accumulated other comprehensive income (loss)	110	(74)
Retained earnings	47,609	60,649
Total stockholders' equity	428,137	433,206
Total liabilities and stockholders' equity	$ 509,256	$ 548,285

Condensed Statements of Operati

Condensed Statements of Operations - USD ($) shares in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Income Statement [Abstract]
Collaboration revenue	$ 6,520,000	$ 4,287,000
Operating expenses:
Research and development	18,278,000	11,211,000
General and administrative	8,635,000	4,220,000
Total operating expenses	26,913,000	15,431,000
Loss from operations	(20,393,000)	(11,144,000)
Interest income	536,000	108,000
Loss before income tax	(19,857,000)	(11,036,000)
Income tax benefit	6,817,000	0
Net loss	$ (13,040,000)	$ (11,036,000)
Basic and diluted net loss per common share	$ (0.49)	$ (0.44)
Weighted-average shares used to compute basic and diluted net loss per common share	26,351	25,072

Condensed Statements of Compreh

Condensed Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (13,040)	$ (11,036)
Other comprehensive income:
Net unrealized gain on marketable securities, net of tax	184	30
Comprehensive loss	$ (12,856)	$ (11,006)

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating activities
Net loss	$ (13,040)	$ (11,036)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	375	400
Stock-based compensation expense	7,401	991
Excess tax benefits from employee equity incentive plans	(1,233)
Deferred income taxes	1,769
Amortization of premium on marketable securities	1,119	534
Changes in operating assets and liabilities:
Receivables from collaborative partners	2,294	277
Income tax receivable	(822)
Prepaid, other current assets, and other long-term assets	756	(689)
Accounts payable	(874)	(192)
Accrued personnel-related expenses	(3,030)	(1,950)
Deferred revenue	(4,648)	82
Deferred rent	(192)	(50)
Income tax payable	(22,367)
Other accrued liabilities and other long-term liabilities	(1,616)	1,081
Net cash used in operating activities	(34,108)	(10,552)
Investing activities
Purchases of marketable securities	(100,665)	(93,876)
Maturities of marketable securities	118,250	24,500
Purchases of property and equipment	(823)	(436)
Net cash provided by (used in) investing activities	16,762	(69,812)
Financing activities
Proceeds from public offering of common stock, net		78,693
Proceeds from issuance of common stock under equity incentive plans	2,755	886
Repurchase of shares to satisfy tax withholding	(3,602)
Excess tax benefits from employee equity incentive plans	1,233
Net cash provided by financing activities	386	79,579
Net decrease in cash and cash equivalents	(16,960)	(785)
Cash and cash equivalents at beginning of period	149,971	15,267
Cash and cash equivalents at end of period	133,011	$ 14,482
Supplemental cash flow information
Cash paid for income taxes	$ 14,701

Description of Business

Description of Business	3 Months Ended
	Mar. 31, 2016
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 novel protein therapeutics. Protein therapeutics are antibodies or drugs developed from extracellular proteins or protein fragments that block disease processes, including cancer and inflammatory diseases. 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 March 31, 2016 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, 2015 filed with the U.S. Securities and Exchange Commission.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2016
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 reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements as well as reported amounts of revenue and expenses during the reporting period. 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, 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. 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 Level 3 securities as of March 31, 2016. The following table summarizes, for assets recorded at fair value, the respective fair values and the classifications by level of input within the fair value hierarchy defined above (in thousands): March 31, 2016 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 126,007 $ 126,007 $ — $ — U.S. Treasury securities 348,807 348,807 — — Total cash equivalents and marketable securities $ 474,814 $ 474,814 $ — $ — December 31, 2015 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 34,821 $ 34,821 $ — $ — U.S. Treasury securities 477,125 477,125 — — Total cash equivalents and marketable securities $ 511,946 $ 511,946 $ — $ — 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 options to purchase shares of common stock and restricted stock awards, or RSAs, (in thousands) from the calculation of diluted net loss per share for all periods presented as the effect would have been antidilutive: Three Months Ended March 31, 2016 2015 Options to purchase common stock 2,918 2,667 RSAs 1,505 — 4,423 2,667 Recently Issued Accounting Standards In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, 2014-09, Revenue from Contracts with Customers: Topic 606 In February 2016, FASB issued ASU 2016-02, Leases. all annual and interim reporting periods thereafter. E In March 2016, FASB issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting This standard makes several modifications to Topic 718 related to the accounting for forfeitures, employer tax withholding on share-based compensation and the financial statement presentation of excess tax benefits or deficiencies. ASU 2016-09 also clarifies the statement of cash flows presentation for certain components of share-based awards. The We are currently evaluating the impact that the adoption of ASU 2016-09 will have on our consolidated financial statements and related disclosures.

Cash Equivalents and Marketable

Cash Equivalents and Marketable Securities	3 Months Ended
	Mar. 31, 2016
Cash And Cash Equivalents [Abstract]
Cash Equivalents and Marketable Securities	3. Cash Equivalents and Marketable Securities The following is a summary of our cash equivalents and marketable securities (in thousands): March 31, 2016 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 126,007 $ — $ — $ 126,007 U.S. Treasury securities 348,807 172 (4 ) 348,975 474,814 172 (4 ) 474,982 Less: cash equivalents (126,007 ) — — (126,007 ) Total marketable securities $ 348,807 $ 172 $ (4 ) $ 348,975 December 31, 2015 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 34,821 $ — $ — $ 34,821 U.S. Treasury securities 477,239 13 (127 ) 477,125 512,060 13 (127 ) 511,946 Less: cash equivalents (144,470 ) — 19 (144,451 ) Total marketable securities $ 367,590 $ 13 $ (108 ) $ 367,495 As of March 31, 2016, 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 $ 348,807 $ 348,975 Total marketable securities $ 348,807 $ 348,975 We determined that the gross unrealized losses on our marketable securities as of March 31, 2016 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 March 31, 2016. There were no sales of available-for-sale securities in any of the periods presented.

Equity Incentive Plans

Equity Incentive Plans	3 Months Ended
	Mar. 31, 2016
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 Number of Exercise Price Remaining Shares Per Share Term Balance at December 31, 2015 3,028,714 $ 12.62 Options granted 119,200 $ 34.83 Options exercised (382,185 ) $ 8.16 Options forfeited (71,329 ) $ 14.14 Options expired (27 ) $ 14.93 Balance at March 31, 2016 2,694,373 $ 14.19 Options exercisable 1,289,024 $ 8.33 5.67 We have granted RSAs to certain of our employees. RSAs are share awards that entitle the holder to receive freely tradable shares of our common stock upon vesting and are unforfeitable once fully vested. We based the fair value of RSAs on the closing sales price of our common stock on the grant date. 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, 2015 1,574,870 $ 19.71 RSAs granted 88,630 $ 35.60 RSAs vested (259,676 ) $ 18.88 RSAs forfeited (78,009 ) $ 18.21 Unvested balance at March 31, 2016 1,325,815 $ 21.02 As of March 31, 2016, there were 2,858,577 shares of common stock available for future issuance under our 2013 Omnibus Incentive Plan. Stock-Based Compensation We calculate employee stock-based compensation expense based on awards ultimately expected to vest reduced by estimated forfeitures. We estimate forfeitures at the time of grant and revise forfeitures, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Total stock-based compensation expense recognized was as follows (in thousands): Three Months Ended March 31, 2016 2015 Research and development $ 3,697 $ 509 General and administrative 3,704 482 Total $ 7,401 $ 991 We estimated the fair value of each stock option using the Black-Scholes option-pricing model based on the date of grant of such stock option with the following assumptions: Three Months Ended March 31, 2016 2015 Expected term (years) 6.3 6.1 Expected volatility 74% 73% Risk-free interest rate 1.5% 1.5-1.7% Expected dividend yield 0% 0% As of March 31, 2016, we had $14.6 million of total unrecognized compensation expense related to nonvested employee and director stock options that we expect to recognize over a weighted-average period of 2.7 years. Additionally, we had $19.3 million of total unrecognized compensation expense related to employee and director RSAs that we expect to recognize over a weighted-average period of 1.1 years.

Collaborative Research and Deve

Collaborative Research and Development Agreements	3 Months Ended
	Mar. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaborative Research and Development Agreements	5. Collaborative Research and Development Agreements GlaxoSmithKline Respiratory Diseases Collaboration In January 2016, we amended our research collaboration and license agreement, referred to as the respiratory diseases collaboration, with GlaxoSmithKline, or GSK, that we originally entered into in April 2012 to identify new therapeutic approaches to treat refractory asthma and chronic obstructive pulmonary disease function. The amendment extended the research term by three months to July 2016 to allow for the conduct of additional activities to validate protein targets we discovered in our screens and increased the research funding that GSK is obligated to pay us under the collaboration by $0.7 million. We are amortizing the additional research funding over the remaining research period. Due to the amendment, we revised our estimate of our substantive performance period under this collaboration to extend through the end of this additional research term and began recognizing the remaining unamortized portion of the upfront payment over this revised period into July 2016. FP-1039 License and Collaboration In March 2016, GSK delivered to us written notice of termination of our license and collaboration agreement with Human Genome Sciences, Inc., which was acquired by GSK in 2012, or the FP-1039 license, for convenience. Pursuant to the terms of the FP-1039 license, termination of the FP-1039 license will become effective on September 5, 2016, which is 180 days after GSK’s notice of termination. Pursuant to the terms of the FP-1039 license, in April 2016, we elected to have GSK complete the conduct of the Phase 1b clinical trial of FP-1039 that GSK is currently conducting, at GSK’s expense.

Employee Benefit Plans

Employee Benefit Plans	3 Months Ended
	Mar. 31, 2016
Postemployment Benefits [Abstract]
Employee Benefit Plans	6 . Employee Benefit Plans We sponsor a 401(k) plan under which eligible employees may elect to contribute to the 401(k) plan, subject to certain limitations, up to the lesser of the statutory maximum or 100% of eligible compensation on a pre-tax basis. We pay the administrative costs for the plan. Effective January 1, 2015, we elected to match employee contributions to the 401(k) plan, or the Company Match, as permitted by the plan. We make matching contributions every pay period in an amount equal to 50% of the amount contributed by the employee up to an annual maximum Company Match per employee equal to $6,000. We have recorded 401(k) plan Company Match expense of $245,000 and $179,000 for the three months ended March 31, 2016 and 2015, respectively.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	7 . Income Taxes We realized an income tax benefit of $6.8 million for the three months ended March 31, 2016 as compared to no tax expense for the three months ended March 31, 2015. The income tax benefit represents our ability to recover taxes accrued in 2015 based on existing tax law that allows us to carryback our 2016 or 2017 tax losses and or credits to recover prior taxes. The income tax benefit is based on the annual effective tax rate method and considers 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. At the end of December 2015, we recognized approximately $15.1 million of net deferred tax assets based on our review of the reversal pattern of these deferred tax assets that may result in future recovery of tax paid in 2015. Based on our forecasted loss for 2016, we assessed the recoverability of deferred tax assets based on their reversal patterns. We will periodically review our ability to realize our deferred tax assets and any adjustment to this recoverability will impact our annual effective tax rate.

Summary of Significant Accoun13

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2016
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 reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements as well as reported amounts of revenue and expenses during the reporting period. 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, 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. 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 Level 3 securities as of March 31, 2016. The following table summarizes, for assets recorded at fair value, the respective fair values and the classifications by level of input within the fair value hierarchy defined above (in thousands): March 31, 2016 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 126,007 $ 126,007 $ — $ — U.S. Treasury securities 348,807 348,807 — — Total cash equivalents and marketable securities $ 474,814 $ 474,814 $ — $ — December 31, 2015 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 34,821 $ 34,821 $ — $ — U.S. Treasury securities 477,125 477,125 — — Total cash equivalents and marketable securities $ 511,946 $ 511,946 $ — $ —
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 options to purchase shares of common stock and restricted stock awards, or RSAs, (in thousands) from the calculation of diluted net loss per share for all periods presented as the effect would have been antidilutive: Three Months Ended March 31, 2016 2015 Options to purchase common stock 2,918 2,667 RSAs 1,505 — 4,423 2,667
Recently Issued Accounting Standards	Recently Issued Accounting Standards In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, 2014-09, Revenue from Contracts with Customers: Topic 606 In February 2016, FASB issued ASU 2016-02, Leases. all annual and interim reporting periods thereafter. E In March 2016, FASB issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting This standard makes several modifications to Topic 718 related to the accounting for forfeitures, employer tax withholding on share-based compensation and the financial statement presentation of excess tax benefits or deficiencies. ASU 2016-09 also clarifies the statement of cash flows presentation for certain components of share-based awards. The We are currently evaluating the impact that the adoption of ASU 2016-09 will have on our consolidated financial statements and related disclosures.

Summary of Significant Accoun14

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2016
Accounting Policies [Abstract]
Summary of Assets Recorded at Fair Value	The following table summarizes, for assets recorded at fair value, the respective fair values and the classifications by level of input within the fair value hierarchy defined above (in thousands): March 31, 2016 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 126,007 $ 126,007 $ — $ — U.S. Treasury securities 348,807 348,807 — — Total cash equivalents and marketable securities $ 474,814 $ 474,814 $ — $ — December 31, 2015 Basis of Fair Value Measurements Total Level 1 Level 2 Level 3 Assets Money market funds $ 34,821 $ 34,821 $ — $ — U.S. Treasury securities 477,125 477,125 — — Total cash equivalents and marketable securities $ 511,946 $ 511,946 $ — $ —
Options and Restricted Stock Awards Excluded from Calculation of Diluted Net Loss Per Share	We excluded the following options to purchase shares of common stock and restricted stock awards, or RSAs, (in thousands) from the calculation of diluted net loss per share for all periods presented as the effect would have been antidilutive: Three Months Ended March 31, 2016 2015 Options to purchase common stock 2,918 2,667 RSAs 1,505 — 4,423 2,667

Cash Equivalents and Marketab15

Cash Equivalents and Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2016
Cash And Cash Equivalents [Abstract]
Summary of Cash Equivalents and Marketable Securities	The following is a summary of our cash equivalents and marketable securities (in thousands): March 31, 2016 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 126,007 $ — $ — $ 126,007 U.S. Treasury securities 348,807 172 (4 ) 348,975 474,814 172 (4 ) 474,982 Less: cash equivalents (126,007 ) — — (126,007 ) Total marketable securities $ 348,807 $ 172 $ (4 ) $ 348,975 December 31, 2015 Amortized Unrealized Unrealized Estimated Cost Basis Gains Losses Fair Value Money market funds $ 34,821 $ — $ — $ 34,821 U.S. Treasury securities 477,239 13 (127 ) 477,125 512,060 13 (127 ) 511,946 Less: cash equivalents (144,470 ) — 19 (144,451 ) Total marketable securities $ 367,590 $ 13 $ (108 ) $ 367,495
Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturity	As of March 31, 2016, 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 $ 348,807 $ 348,975 Total marketable securities $ 348,807 $ 348,975

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	3 Months Ended
	Mar. 31, 2016
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 Number of Exercise Price Remaining Shares Per Share Term Balance at December 31, 2015 3,028,714 $ 12.62 Options granted 119,200 $ 34.83 Options exercised (382,185 ) $ 8.16 Options forfeited (71,329 ) $ 14.14 Options expired (27 ) $ 14.93 Balance at March 31, 2016 2,694,373 $ 14.19 Options exercisable 1,289,024 $ 8.33 5.67
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, 2015 1,574,870 $ 19.71 RSAs granted 88,630 $ 35.60 RSAs vested (259,676 ) $ 18.88 RSAs forfeited (78,009 ) $ 18.21 Unvested balance at March 31, 2016 1,325,815 $ 21.02
Schedule of Stock-Based Compensation Expenses Recognized	Total stock-based compensation expense recognized was as follows (in thousands) Three Months Ended March 31, 2016 2015 Research and development $ 3,697 $ 509 General and administrative 3,704 482 Total $ 7,401 $ 991
Schedule of Stock Option Weighted-Average Assumptions	We estimated the fair value of each stock option using the Black-Scholes option-pricing model based on the date of grant of such stock option with the following assumptions: Three Months Ended March 31, 2016 2015 Expected term (years) 6.3 6.1 Expected volatility 74% 73% Risk-free interest rate 1.5% 1.5-1.7% Expected dividend yield 0% 0%

Description of Business - Addit

Description of Business - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2016Segment
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of operating segment	1

Summary of Significant Accoun18

Summary of Significant Accounting Policies - Summary of Assets Recorded at Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Assets
U.S. Treasury securities	$ 348,975	$ 367,495
Total cash equivalents and marketable securities	474,814	511,946
Money market funds [Member]
Assets
Money market funds	126,007	34,821
U.S. Treasury securities	126,007	34,821
U.S. Treasury securities [Member]
Assets
U.S. Treasury securities	348,807	477,125
Level 1 [Member]
Assets
Total cash equivalents and marketable securities	474,814	511,946
Level 1 [Member] | Money market funds [Member]
Assets
Money market funds	126,007	34,821
Level 1 [Member] | U.S. Treasury securities [Member]
Assets
U.S. Treasury securities	$ 348,807	$ 477,125

Summary of Significant Accoun19

Summary of Significant Accounting Policies - Options and Restricted Stock Awards Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net (loss) income per share	4,423	2,667
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) income per share	2,918	2,667
RSAs [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted net (loss) income per share	1,505

Cash Equivalents and Marketab20

Cash Equivalents and Marketable Securities - Summary of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	$ 348,807	$ 367,590
Unrealized Gains	172	13
Unrealized Losses	(4)	(108)
Estimated Fair Value	348,975	367,495
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	126,007	34,821
Estimated Fair Value	126,007	34,821
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	348,807	477,239
Unrealized Gains	172	13
Unrealized Losses	(4)	(127)
Estimated Fair Value	348,975	477,125
Marketable securities including cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	474,814	512,060
Unrealized Gains	172	13
Unrealized Losses	(4)	(127)
Estimated Fair Value	474,982	511,946
Cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	(126,007)	(144,470)
Unrealized Losses		19
Estimated Fair Value	$ (126,007)	$ (144,451)

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	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	$ 348,807	$ 367,590
Total marketable securities, Estimated Fair Value	348,975	367,495
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, In one year or less	348,807
Amortized Cost Basis	348,807	477,239
Estimated Fair Value, In one year or less	348,975
Total marketable securities, Estimated Fair Value	$ 348,975	$ 477,125

Cash Equivalents and Marketab22

Cash Equivalents and Marketable Securities - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2016USD ($)
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)	3 Months Ended
	Mar. 31, 2016$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning balance | shares	3,028,714
Number of Shares, Options granted | shares	119,200
Number of Shares, Options exercised | shares	(382,185)
Number of Shares, Options forfeited | shares	(71,329)
Number of Shares, Options expired | shares	(27)
Number of Shares, Ending balance | shares	2,694,373
Number of Shares, Options exercisable | shares	1,289,024
Weighted-Average Exercise Price Per Share, Options beginning balance | $ / shares	$ 12.62
Weighted-Average Exercise Price Per Share, Options granted | $ / shares	34.83
Weighted-Average Exercise Price Per Share, Options exercised | $ / shares	8.16
Weighted-Average Exercise Price Per Share, Options forfeited | $ / shares	14.14
Weighted-Average Exercise Price Per Share, Options expired | $ / shares	14.93
Weighted-Average Exercise Price Per Share, Options ending balance | $ / shares	14.19
Weighted-Average Exercise Price Per Share, Options exercisable | $ / shares	$ 8.33
Weighted-Average Remaining Contractual Terms, Options exercisable	5 years 8 months 1 day

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]	3 Months Ended
	Mar. 31, 2016$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Unvested, Beginning balance | shares	1,574,870
Granted, Number of Shares | shares	88,630
Vested, Number of Shares | shares	(259,676)
Forfeited, Number of Shares | shares	(78,009)
Number of Shares, Unvested, Ending balance | shares	1,325,815
Shares, Weighted-Average Grant-Date Fair Value balance at December 31, 2015 | $ / shares	$ 19.71
Shares Granted, Weighted-Average Grant-Date Fair Value | $ / shares	35.60
Shares Vested, Weighted-Average Grant-Date Fair Value | $ / shares	18.88
Shares Forfeited, Weighted-Average Grant-Date Fair Value | $ / shares	18.21
Shares, Weighted-Average Grant-Date Fair Value balance at March 31, 2016 | $ / shares	$ 21.02

Equity Incentive Plans - Additi

Equity Incentive Plans - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2016USD ($)shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to nonvested employee and director stock options	$ 14.6
Unrecognized compensation expense expected to recognize, weighted-average period	2 years 8 months 12 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	1 year 1 month 6 days
Total unrecognized compensation expense related to employee and director RSAs	$ 19.3
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	2,858,577

Equity Incentive Plans - Sche26

Equity Incentive Plans - Schedule of Stock-Based Compensation Expenses Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	$ 7,401	$ 991
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	3,697	509
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense recognized	$ 3,704	$ 482

Equity Incentive Plans - Sche27

Equity Incentive Plans - Schedule of Stock Option Assumptions (Detail) - Options [Member]	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (years)	6 years 3 months 18 days	6 years 1 month 6 days
Expected volatility	74.00%	73.00%
Risk-free interest rate	1.50%
Risk-free interest rate, minimum		1.50%
Risk-free interest rate, maximum		1.70%
Expected dividend yield	0.00%	0.00%

Collaborative Research and De28

Collaborative Research and Development Agreements - Additional Information (Detail) - Glaxo Smith Kline LLC [Member] - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Jan. 31, 2016	Mar. 31, 2016
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Increase the research funding	$ 0.7
Extend research terms	3 months
Extend research date	2016-07
FP-1039 License and Collaboration [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Termination license agreement effective date		Sep. 5, 2016
Notice period of termination of license agreement		180 days

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail) - USD ($)	Jan. 02, 2015	Mar. 31, 2016	Mar. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Eligible employees contribution percentage		100.00%
Defined contribution plan, employer matching contribution, percent of match	50.00%
Defined contribution plan, employer matching contribution, amount	$ 6,000
Defined contribution plan, company matching contribution expense		$ 245,000	$ 179,000

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income tax (benefit) expense	$ (6,817,000)	$ 0
Net deferred tax assets			$ 15,100,000