Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Additional Information (Detail)

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Stockholders' Equity - Additional Information (Detail) - USD ($)
 1 Months Ended 12 Months Ended
Aug. 01, 2017
Jun. 23, 2017
Dec. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Class Of Warrant Or Right [Line Items]              
Warrant exercise price $ 39.82       $ 3.07 $ 3.07 $ 3.07
Warrants to purchase shares of common stock 377,273   377,273 377,273 17,310 17,310 14,254
Common Stock | 2017 Warrants              
Class Of Warrant Or Right [Line Items]              
Warrant exercise price     $ 39.82 $ 39.82      
Warrants to purchase shares of common stock     377,273 377,273      
Preferred Stock | 2014 Warrants              
Class Of Warrant Or Right [Line Items]              
Warrant exercise price         $ 3.07    
Warrants to purchase shares of common stock         48,874    
Concurrent Financing              
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   $ 6.8423          
Warrants              
Class Of Warrant Or Right [Line Items]              
Change in fair value of common stock warrants       $ 128,000      
Wedbush Agreement | PIPE Financing | Common Stock              
Class Of Warrant Or Right [Line Items]              
Warrant exercisable period     7 years        
Warrant exercise price     $ 6.8423 $ 6.8423      
Warrants to purchase shares of common stock     57,930 57,930      
Private Placement | Longitude Venture Partners III, L..P. | PIPE Financing              
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 0.5            
Sale of units, description and its composition       the Company sold an aggregate of 5,793,063 units (the “Units”) having an aggregate purchase price of $40.0 million (“PIPE Financing”), each such Unit consisting of (i) one (1) share (the “Shares”) of our common stock and (ii) a warrant (the “Warrants”) to purchase 0.5 shares of our common stock (the “Private Placement”).      
Purchase price per unit $ 6.9048            
Warrant exercisable period 7 years            
Warrant exercise price $ 6.8423            
Warrants to purchase shares of common stock     2,896,532 2,896,532