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
Aug. 01, 2017
Jun. 23, 2017
Sep. 30, 2017
Dec. 31, 2016
Class Of Warrant Or Right [Line Items]        
Warrants to purchase shares of common stock     377,273  
Warrants        
Class Of Warrant Or Right [Line Items]        
Change in fair value of common stock warrants     $ 272,000  
2017 Warrants | Common Stock        
Class Of Warrant Or Right [Line Items]        
Warrants to purchase shares of common stock     377,273  
Warrant exercise price     $ 39.82  
2014 Warrants | Preferred Stock        
Class Of Warrant Or Right [Line Items]        
Warrants to purchase shares of common stock       48,874
Warrant exercise price       $ 3.07
Takeda Pharmaceuticals Inc        
Class Of Warrant Or Right [Line Items]        
Aggregate purchase price   $ 20,000,000    
Each unit of shares transaction of common stock   2,922,993    
Purchase price per share   $ 6.84    
Private Placement | Longitude Venture Partners III, L..P.        
Class Of Warrant Or Right [Line Items]        
Number of aggregate units sold 5,793,063      
Aggregate purchase price $ 40,000,000      
Each unit of shares transaction of common stock 1      
Warrants to purchase shares of common stock 2,896,532   2,896,532  
Purchase price per unit $ 6.9048      
Warrant exercisable period 7 years      
Warrant exercise price $ 6.8423