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Stockholders' Equity - Additional Information (Detail) - USD ($) | 1 Months Ended | 12 Months Ended
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Jun. 30, 2017 | Aug. 31, 2016 | Jun. 30, 2016 | Apr. 30, 2016 | Jan. 31, 2016 | Jun. 30, 2015 | Dec. 31, 2012 | Jan. 31, 2011 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2010
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds from sale of common stock |  | $ 215,900,000 |  |  | $ 281,600,000 |  |  |  | $ 31,188,000 | $ 518,896,000 | $ 14,547,000 |  |  |
Share of common stock issued |  | 6,969,696 |  |  | 10,344,827 |  | 19,000,000 | 12,565,446 |  |  |  |  |  |
Common stock, par value |  |  |  |  |  |  |  |  | $ 0.0001 | $ 0.0001 |  |  |  |
Value of shares purchased by Baker Entities in public offerings |  |  |  |  |  |  |  |  | $ 12,000 | $ 12,000 |  |  |  |
Proceed from sale of stock and warrants |  |  |  |  |  |  | $ 80,500,000 | $ 13,900,000 |  |  |  |  |  |
Common stock sale price per share |  |  |  |  |  |  | $ 4.43 | $ 1.19375 |  |  |  |  |  |
Warrants exercised for purchase of common shares |  |  |  |  |  |  |  |  | 1,465,968 |  |  | 1,759,162 | 1,172,774 |
Issuance of common stock from exercise of warrants on a net issuance basis (in shares) |  |  |  |  |  |  |  |  | 1,408,570 |  |  | 1,643,006 | 874,719 |
Closing market price of Common stock |  |  |  |  |  |  |  |  | $ 30.11 |  |  |  |  |
Aggregate intrinsic value of stock options exercised |  |  |  |  |  |  |  |  | $ 24,400,000 | $ 43,200,000 | $ 55,900,000 |  |  |
Cash received from options exercised |  |  |  |  |  |  |  |  | $ 26,700,000 |  |  |  |  |
Weighted average per share fair value of options granted |  |  |  |  |  |  |  |  | $ 21.11 | $ 17.65 | $ 25.80 |  |  |
Unrecognized compensation costs |  |  |  |  |  |  |  |  | $ 206,500,000 |  |  |  |  |
Weighted average period cost expected to be recognized |  |  |  |  |  |  |  |  | 3 years 2 months 8 days |  |  |  |  |
Issuance of common stock pursuant to employee stock purchase plan |  |  |  |  |  |  |  |  | $ 4,522,000 | $ 3,131,000 | $ 1,556,000 |  |  |
Payment received from stockholder pursuant to a settlement agreement related to short-swing profits |  |  |  | $ 14,300,000 |  |  |  |  |  | $ 14,320,000 |  |  |  |
Prior stockholders percentage of equity holding |  |  |  | 10.00% |  |  |  |  |  |  |  |  |  |
Stock Options | Equity Incentive Plan 2010 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise price of Options as percentage of fair market value |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00%
Options maximum expiration term |  |  |  |  |  |  |  |  |  |  |  |  |  | 10 years
Options vesting period |  |  |  |  |  |  |  |  |  |  |  |  |  | 4 years
Number of common stock authorized for issuance |  |  |  |  |  |  |  |  | 25,997,247 |  |  |  |  |
Common stock available for grants |  |  |  |  |  |  |  |  | 8,053,811 |  |  |  |  |
Common stock reserved for issuance under stock purchase plan | 5,500,000 |  | 3,000,000 |  |  | 5,000,000 |  |  |  |  |  |  |  |
Stock Options | Equity Incentive Plan 2004 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise price of Options as percentage of fair market value |  |  |  |  |  |  |  |  | 100.00% |  |  |  |  |
Options vesting period |  |  |  |  |  |  |  |  | 4 years |  |  |  |  |
Number of periods additional number of shares could be added to shares authorized for issuance |  |  |  |  |  |  |  |  | 10 years |  |  |  |  |
Employee Stock Purchase Plan |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of common stock authorized for issuance |  |  |  |  |  |  |  |  | 1,925,000 |  |  |  |  |
Common stock reserved for issuance under stock purchase plan |  |  | 400,000 |  |  |  |  |  |  |  |  |  |  |
Term of ESPP Evergreen Provision |  |  |  |  |  |  |  |  | 10 years |  |  |  |  |
Common stock remained available for issuance pursuant to the Purchase Plan |  |  |  |  |  |  |  |  | 388,011 |  |  |  |  |
Eligible employees percentage of earnings withheld to purchase shares under purchase plan |  |  |  |  |  |  |  |  | 15.00% |  |  |  |  |
Purchase price of common stock as percentage of market value |  |  |  |  |  |  |  |  | 85.00% |  |  |  |  |
Issuance of common stock pursuant to employee stock purchase plan |  |  |  |  |  |  |  |  | 192,402 | 136,283 | 68,793 |  |  |
Average per share price of stock issued under purchase plan |  |  |  |  |  |  |  |  | $ 23.50 | $ 22.97 | $ 22.62 |  |  |
Weighted average per share fair value of purchase rights granted |  |  |  |  |  |  |  |  | $ 11.44 | $ 12.34 | $ 14.31 |  |  |
Issuance of common stock pursuant to employee stock purchase plan |  |  |  |  |  |  |  |  | $ 4,500,000 | $ 3,100,000 | $ 1,600,000 |  |  |
Expire on December 17, 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Warrants issued |  |  |  |  |  |  | 500,000 |  |  |  |  |  | 500,000 |
Warrants issuance price per share |  |  |  |  |  |  | $ 4.42 |  |  |  |  |  |  |
Warrant exercise price |  |  |  |  |  |  | $ 0.01 |  |  |  |  |  | $ 0.01 |
Warrant expiration date |  |  |  |  |  |  |  |  | Dec. 17, 2019 |  |  |  |  |
Issuance of warrant value |  |  |  |  |  |  | $ 2,200,000 |  |  |  |  |  |  |
Warrant risk free interest rate |  |  |  |  |  |  | 1.10% |  |  |  |  |  |  |
volatility percentage |  |  |  |  |  |  | 105.80% |  |  |  |  |  |  |
Warrant term |  |  |  |  |  |  | 7 years |  |  |  |  |  |  |
Warrants outstanding |  |  |  |  |  |  |  |  | 500,000 |  |  |  |  |
Description of warrant |  |  |  |  |  |  |  |  | Per their terms, the warrants to purchase 500,000 shares of common stock, all of which remained outstanding at December 31, 2017, may not be exercised if the holder’s ownership of the Company’s common stock would exceed 19.99 percent following such exercise. |  |  |  |  |
Dividend yield |  |  |  |  |  |  | 0.00% |  |  |  |  |  |  |
Expired on January 11, 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Warrant exercise price |  |  |  |  |  |  |  | $ 1.38 |  |  |  |  |  |
Warrant expiration date |  |  |  |  |  |  |  |  | Jan. 11, 2018 |  |  |  |  |
Issuance of warrant value |  |  |  |  |  |  |  | $ 3,300,000 |  |  |  |  |  |
Warrant risk free interest rate |  |  |  |  |  |  |  | 2.80% |  |  |  |  |  |
volatility percentage |  |  |  |  |  |  |  | 99.00% |  |  |  |  |  |
Warrant term |  |  |  |  |  |  |  | 7 years |  |  |  |  |  |
Number of common stock per unit sold |  |  |  |  |  |  |  | 1 |  |  |  |  |  |
Dividend yield |  |  |  |  |  |  |  | 0.00% |  |  |  |  |  |
Number of common stock allowed to purchase |  |  |  |  |  |  |  | 0.35 |  |  |  |  |  |
Warrants outstanding to purchase common stock |  |  |  |  |  |  |  |  | 0 |  |  |  |  |
Registration Rights Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, par value |  |  |  |  | $ 0.0001 |  |  |  |  |  |  |  |  |
Expiration period |  |  |  |  | 10 years |  |  |  |  |  |  |  |  |
Maximum amount of expense agreed to bear under the agreement |  |  |  |  | $ 50,000 |  |  |  |  |  |  |  |  |
Registration Rights Agreement | Baker Brothers Life Sciences L.P. |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Value of shares purchased by Baker Entities in public offerings |  | $ 43,000,000 |  |  | $ 75,000,000 |  |  |  |  |  |  |  |  |
Option To Purchase Additional Shares |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share of common stock issued |  | 909,090 |  |  |  |  |  |  |  |  |  |  |  |

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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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