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Stockholders' Equity - Additional Information (Detail) - USD ($)
3 Months Ended
Mar. 31, 2016
Jun. 16, 2015
Mar. 31, 2015
Dec. 04, 2006
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Maximum percentage before exercise       20.00%
Number of shares available for issuance 5,700,000      
Employee share purchase plan, percentage of fair market value of common stock at beginning of offering period 85.00%      
Employee share purchase plan, percentage of fair market value of common stock on purchase date 85.00%      
Eligible employee contributions $ 25,000      
Shares issued in period 397,536      
Performance Share Units [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of PSU's granted 129,150      
Period after performance is achieved to earn portion of eligible shares under award 1 year      
Revenue Goals [Member] | Performance Share Units [Member] | Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Payout percentage of PSUs 50.00%      
Revenue Goals [Member] | Performance Share Units [Member] | Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Payout percentage of PSUs 150.00%      
Clinical Development Milestones [Member] | Performance Share Units [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Payout percentage of PSUs 100.00%      
Equity Incentive Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares authorized for issuance   47,700,000 42,300,000  
ESPP [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares authorized for issuance 6,000,000