Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Additional Information (Detail)

v3.8.0.1
Stockholders' Equity - Additional Information (Detail) - USD ($)
 3 Months Ended
Mar. 12, 2018
Mar. 31, 2018
Mar. 31, 2017
Feb. 12, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Employee Stock Purchase Plan to eligible employees, compensation expense recognized   $ 38,000 $ 35,000  
Share-based Compensation   5,053,000 2,929,000  
Adjustments To Additional Paid In Capital At Market Offering Costs   $ (6,000)    
Market Offering [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Shares Issued, Price Per Share   $ 4.92    
Proceeds from issuance of Common stock   $ 300,000    
Issuance of Common Stock for At the Market Offering in shares   64,797    
Adjustments To Additional Paid In Capital At Market Offering Costs   $ 5,700    
Checkpoint [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Shares Issued, Price Per Share       $ 4.35
Proceeds from issuance of Common stock $ 20,800,000      
Stock Issued During Period, Shares, New Issues 5,290,000      
Stock Issued During Period, Value, New Issues $ 23,000,000      
Payments of Stock Issuance Costs $ 2,200,000      
Research and Development Expense [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Allocated Share-based Compensation Expense   2,300,000 800,000  
General and Administrative Expense [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Allocated Share-based Compensation Expense   $ 2,700,000 $ 2,100,000  
Restricted Stock [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition   3 years 1 month 6 days    
Share-based Compensation   $ 8,400,000    
Restricted Stock Units (RSUs) [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition     2 years 9 months 18 days  
Share-based Compensation     $ 3,400,000  
Employee Stock Option [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Employee Stock Purchase Plan to eligible employees, Reckoning fair value percentage during offering period   85.00%    
Common Stock issued in connection with the first ESPP offering   245,652    
Common Stock, Capital Shares Reserved for Future Issuance   154,348