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Stockholders' Equity - Additional Information (Detail) - USD ($)
 1 Months Ended 12 Months Ended
Nov. 30, 2018
Jun. 30, 2018
Jun. 30, 2017
Aug. 31, 2016
Jun. 30, 2016
Apr. 30, 2016
Jan. 31, 2016
Jun. 30, 2015
Dec. 31, 2012
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2010
Class of Stock [Line Items]                          
Net proceeds from sale of common stock $ 298,500,000     $ 215,900,000     $ 281,600,000     $ 306,647,000 $ 31,188,000 $ 518,896,000  
Share of common stock issued 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                   $ 14,000 $ 12,000    
Proceed from sale of stock and warrants                 $ 80,500,000        
Common stock sale price per share                 $ 4.43        
Options vesting period                   4 years      
Closing market price of Common stock                   $ 16.17      
Aggregate intrinsic value of stock options exercised                   $ 11,200,000 $ 24,400,000 $ 43,200,000  
Cash received from options exercised                   $ 4,400,000      
Weighted average per share fair value of options granted                   $ 12.14 $ 21.11 $ 17.65  
Unrecognized compensation costs                   $ 153,700,000      
Weighted average period cost expected to be recognized                   3 years 21 days      
Issuance of common stock pursuant to employee stock purchase plan                   $ 3,682,000 $ 4,522,000 $ 3,131,000  
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                   26,919,256      
Common stock available for grants                   6,676,769      
Common stock reserved for issuance under stock purchase plan   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 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                   $ 7,500,000      
Weighted average period cost expected to be recognized                   3 years 9 months 18 days      
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                   154,291      
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                   233,720 192,402 136,283  
Average per share price of stock issued under purchase plan                   $ 15.75 $ 23.50 $ 22.97  
Weighted average per share fair value of purchase rights granted                   $ 8.25 $ 11.44 $ 12.34  
Issuance of common stock pursuant to employee stock purchase plan                   $ 3,700,000 $ 4,500,000 $ 3,100,000  
Expire on December 17, 2019                          
Class of Stock [Line Items]                          
Warrants issued                 500,000        
Warrants issuance price per share                 $ 4.42        
Warrant exercise price                 $ 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, of which 493,145 remained outstanding at December 31, 2018, 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%        
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 2,426,470     909,090