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Stockholders' Equity - Additional Information (Detail) - USD ($)
 1 Months Ended 12 Months Ended
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