Quarterly report pursuant to Section 13 or 15(d)

Financial Instruments - Additional Information (Detail)

v3.10.0.1
Financial Instruments - Additional Information (Detail) - USD ($)
 1 Months Ended 3 Months Ended 9 Months Ended 12 Months Ended
Apr. 30, 2018
May 31, 2017
Sep. 30, 2018
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2016
Dec. 31, 2017
Mar. 31, 2017
Schedule of Available-for-sale Securities [Line Items]                
Marketable securities maturity period       1 year        
Warrants to purchase common stock     1,297,151 1,297,151     1,524,573  
Change in fair value of warrant liability       $ (93,000) $ (7,114,000)      
Financial instruments fair value transfers between Level 1, Level 2 or Level 3     $ 0 0        
Initial Public Offering [Member]                
Schedule of Available-for-sale Securities [Line Items]                
Shares price per share   $ 15.00       $ 15.00    
Convertible Notes Payable [Member] | Acacia [Member]                
Schedule of Available-for-sale Securities [Line Items]                
Number of warrants issued           3    
Warrants maturity period           4 years    
Acacia Note Warrants [Member]                
Schedule of Available-for-sale Securities [Line Items]                
Warrants to purchase common stock           51,437    
Primary Warrant [Member] | Acacia [Member]                
Schedule of Available-for-sale Securities [Line Items]                
Warrants maturity period           5 years    
Primary Warrant [Member] | Acacia [Member] | Initial Public Offering [Member]                
Schedule of Available-for-sale Securities [Line Items]                
Warrant exercise price   $ 13.6088            
Amended Primary and Acacia Note Warrants [Member] | Initial Public Offering [Member]                
Schedule of Available-for-sale Securities [Line Items]                
Warrant exercise price               $ 13.6088
10% Warrant [Member] | Acacia [Member]                
Schedule of Available-for-sale Securities [Line Items]                
Warrants maturity period   5 years            
Warrants to purchase common stock   809,400            
Warrant exercise price   $ 13.6088            
Warrant, percentage   10.00%            
10% Warrant [Member] | Acacia [Member] | Fair Value, Inputs, Level 3 [Member]                
Schedule of Available-for-sale Securities [Line Items]                
Warrant, percentage   10.00%            
Fair value of warrant   $ 5,790,000            
April 2018 Warrant [Member]                
Schedule of Available-for-sale Securities [Line Items]                
Warrants maturity period 5 years              
Warrants to purchase common stock 20,000              
Warrant exercise price $ 11.73              
Fair value of warrant     114,000 114,000        
Change in fair value of warrant liability     $ 93,000 $ 93,000