Collaborations - Additional Information (Detail)
$ / shares in Units, $ in Thousands
 1 Months Ended 12 Months Ended
Jan. 30, 2014
shares
Apr. 30, 2012
USD ($)
Sep. 30, 2015
USD ($)
Jun. 30, 2014
USD ($)
Apr. 30, 2013
USD ($)
$ / shares
shares
Apr. 30, 2012
USD ($)
shares
Dec. 31, 2016
USD ($)
Deliverables
shares
Dec. 31, 2015
USD ($)
shares
Dec. 31, 2014
USD ($)
shares
Dec. 31, 2012
USD ($)
Feb. 05, 2014
shares
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                      
License and milestone fee revenue               $ 1,710 $ 302    
Withholding tax             $ (468) (397) (201)    
Collaborative revenue               2,093 2,201    
Clinical compound revenue             $ 86 $ 0 $ 674    
Issuance of convertible preferred stock | shares             0 0 0   29,186,929
Research and development expense             $ 49,253 $ 21,221 $ 15,068    
Convertible Preferred Stock [Member]                      
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                      
Preferred stock converted to common shares, Shares | shares                 (29,186,929)    
Common Stock [Member]                      
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                      
Preferred stock converted to common shares, Shares | shares                 12,554,171    
Chong Kun Dang Pharmaceutical Corporation [Member] | KOREA, REPUBLIC OF                      
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                      
Withholding tax               124   $ 124  
Withholding tax due               83      
Chong Kun Dang Pharmaceutical Corporation [Member] | Common Stock [Member]                      
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                      
Preferred stock converted to common shares, Shares | shares           69,444          
Maruishi Pharmaceutical Co., Ltd. [Member]                      
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                      
Upfront non-refundable, non-creditable license fee         $ 15,000            
License and milestone fee revenue       $ 480       1,084      
Number of deliverables for revenue recognized | Deliverables             2        
Value of arrangement         15,337            
Revenue recognized from non-substantive milestones             $ 8,000        
Revenue recognized from substantive milestones             2,500        
Contractual foreign currency exchange adjustments     $ 275 20              
Collaborative revenue               641      
Amount due from milestone payments net of contractual foreign currency exchange adjustments     $ 1,725                
Stock purchase agreement, purchase price of preferred stock         8,000            
Stock purchase agreement, purchase price fair value of preferred stock         7,663            
Stock purchase agreement, purchase price premium of preferred stock         $ 337            
Clinical trial costs related to the R&D services deliverable             0 1,583 $ 3,000    
Research and development expense                 3,558    
Cost of clinical compound sold to Maruishi                 $ 558    
Maruishi Pharmaceutical Co., Ltd. [Member] | Common Stock [Member]                      
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                      
Preferred stock converted to common shares, Shares | shares 842,105                    
Maruishi Pharmaceutical Co., Ltd. [Member] | Junior A Convertible Preferred Stock [Member] | Convertible Preferred Stock [Member]                      
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                      
Issuance of convertible preferred stock | shares         2,105,263            
Stock purchase agreement, purchase price of preferred stock per share | $ / shares         $ 3.80            
Maruishi Pharmaceutical Co., Ltd. [Member] | Junior A Convertible Preferred Stock [Member] | Convertible Preferred Stock [Member] | Fair Value [Member]                      
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                      
Stock purchase agreement, purchase price of preferred stock per share | $ / shares         $ 3.64            
Maruishi Pharmaceutical Co., Ltd. [Member] | Clinical Development [Member]                      
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                      
Next potential milestone that could be received             $ 1,000        
Maruishi Pharmaceutical Co., Ltd. [Member] | License [Member]                      
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                      
License and milestone fee revenue       302 $ 9,637            
Estimated selling price         10,200            
Maruishi Pharmaceutical Co., Ltd. [Member] | R & D Services [Member]                      
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                      
Estimated selling price         6,200            
Deferred R&D service revenue       90 $ 5,700            
Collaborative revenue       $ 88              
Chong Kun Dang Agreement [Member]                      
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                      
Upfront non-refundable, non-creditable license fee   $ 1,000                  
Milestone payments receivable   3,750       $ 3,750          
License and milestone fee revenue           $ 646   626   $ 626  
Milestone payment receivable               417      
Next potential milestone that could be received               $ 500      
Chong Kun Dang Agreement [Member] | Junior Convertible Preferred Stock [Member] | Convertible Preferred Stock [Member]                      
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                      
Issuance of convertible preferred stock, Shares | shares           173,611          
Issuance of convertible preferred stock, Value           $ 354          
Chong Kun Dang Agreement [Member] | Clinical Development [Member]                      
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                      
Milestone payments receivable   2,250       2,250          
Chong Kun Dang Agreement [Member] | Regulatory Events [Member]                      
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]                      
Milestone payments receivable   $ 1,500       $ 1,500