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Stockholders' Equity - Additional Information (Detail) - USD ($) | 1 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2019 | Jun. 30, 2019 | Nov. 30, 2018 | Jun. 30, 2018 | Jun. 30, 2017 | Aug. 31, 2016 | Jun. 30, 2016 | Jan. 31, 2016 | Jun. 30, 2015 | Dec. 31, 2012 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2010
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net proceeds from sale of common stock | $ 271,500,000 |  | $ 298,500,000 |  |  | $ 215,900,000 |  | $ 281,600,000 |  |  | $ 371,847,000 | $ 306,647,000 | $ 31,188,000 |
Issuance of common stock in public offering, net of issuance costs (in shares) | 7,187,500 |  | 18,602,941 |  |  | 6,969,696 |  | 10,344,827 |  | 19,000,000 |  |  |  |
Common stock, par value |  |  |  |  |  |  |  |  |  |  | $ 0.0001 | $ 0.0001 |  |
Value of shares purchased by Baker Entities in public offerings |  |  |  |  |  |  |  |  |  |  | $ 15,000 | $ 14,000 |  |
Proceed from sale of stock and warrants |  |  |  |  |  |  |  |  |  | $ 80,500,000 |  |  |  |
Common stock sale price per share |  |  |  |  |  |  |  |  |  | $ 4.43 |  |  |  |
Warrants issued |  |  |  |  |  |  |  |  |  | 500,000 |  |  |  |
Warrants issuance price per share |  |  |  |  |  |  |  |  |  | $ 4.42 |  |  |  |
Warrant exercise price |  |  |  |  |  |  |  |  |  | $ 0.01 |  |  |  |
Issuance of warrant value |  |  |  |  |  |  |  |  |  | $ 2,200,000 |  |  |  |
Warrants outstanding |  |  |  |  |  |  |  |  |  | 500,000 | 493,145 |  |  |
Description of warrant |  |  |  |  |  |  |  |  |  |  | Per their terms, the warrants to purchase 500,000 shares of common stock, of which 493,145 remained outstanding at December 31, 2019, may not be exercised if the holder’s ownership of the Company’s common stock would exceed 19.99 percent following such exercise. |  |  |
Options vesting period |  |  |  |  |  |  |  |  |  |  | 4 years |  |  |
Closing market price of Common stock |  |  |  |  |  |  |  |  |  |  | $ 42.78 |  |  |
Aggregate intrinsic value of stock options exercised |  |  |  |  |  |  |  |  |  |  | $ 56,600,000 | $ 11,200,000 | $ 24,400,000 |
Cash received from options exercised |  |  |  |  |  |  |  |  |  |  | $ 96,000,000.0 |  |  |
Weighted average per share fair value of options granted |  |  |  |  |  |  |  |  |  |  | $ 15.97 | $ 12.14 | $ 21.11 |
Unrecognized compensation costs |  |  |  |  |  |  |  |  |  |  | $ 119,300,000 |  |  |
Weighted average period cost expected to be recognized |  |  |  |  |  |  |  |  |  |  | 2 years 9 months 18 days |  |  |
Issuance of common stock pursuant to employee stock purchase plan |  |  |  |  |  |  |  |  |  |  | $ 4,411,000 | $ 3,682,000 | $ 4,522,000 |
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 |  |  |  |  |  |  |  |  |  |  | 31,254,090 |  |  |
Common stock available for grants |  |  |  |  |  |  |  |  |  |  | 12,381,699 |  |  |
Common stock reserved for issuance under stock purchase plan |  | 8,300,000 |  | 6,700,000 | 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 common stock authorized for issuance |  | 600,000 |  |  |  |  |  |  |  |  |  |  |  |
Number of periods additional number of shares could be added to shares authorized for issuance |  |  |  |  |  |  |  |  |  |  | 10 years |  |  |
Restricted Stock Units |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unrecognized compensation costs |  |  |  |  |  |  |  |  |  |  | $ 22,700,000 |  |  |
Weighted average period cost expected to be recognized |  |  |  |  |  |  |  |  |  |  | 3 years 9 months 18 days |  |  |
Weighted average grant date fair value, Granted |  |  |  |  |  |  |  |  |  |  | $ 25.22 | $ 21.07 |  |
Employee Stock Purchase Plan |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of common stock authorized for issuance |  |  |  |  |  |  |  |  |  |  | 2,525,000 |  |  |
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 |  |  |  |  |  |  |  |  |  |  | 485,254 |  |  |
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 |  |  |  |  |  |  |  |  |  |  | 269,037 | 233,720 | 192,402 |
Average per share price of stock issued under purchase plan |  |  |  |  |  |  |  |  |  |  | $ 16.41 | $ 15.75 | $ 23.50 |
Weighted average per share fair value of purchase rights granted |  |  |  |  |  |  |  |  |  |  | $ 14.24 | $ 8.25 | $ 11.44 |
Issuance of common stock pursuant to employee stock purchase plan |  |  |  |  |  |  |  |  |  |  | $ 4,400,000 | $ 3,700,000 | $ 4,500,000 |
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 | $ 62,500,000 |  | $ 200,000,000.0 |  |  | $ 43,000,000.0 |  | $ 75,000,000.0 |  |  |  |  |  |
Option To Purchase Additional Shares |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock in public offering, net of issuance costs (in shares) | 937,500 |  | 2,426,470 |  |  | 909,090 |  |  |  |  |  |  |  |

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