Annual report pursuant to Section 13 and 15(d)

Description of Business - Additional Information (Detail)

v3.8.0.1
Description of Business - Additional Information (Detail) - USD ($)
 1 Months Ended 12 Months Ended
Nov. 21, 2017
May 17, 2017
Nov. 30, 2017
May 31, 2017
Jul. 31, 2014
Dec. 31, 2017
Dec. 31, 2016
May 16, 2017
Organization [Line Items]                
Common stock issued           13,538,080    
Underwriting discounts, commissions and offering costs             $ 136,000  
Net book value             23,350,000  
Cash proceeds from exercise of warrants           $ 29,263,000    
Proceeds from issuance of common stock           $ 56,468,000    
Bridge Loan [Member]                
Organization [Line Items]                
Accrued interest   $ 45,000            
Warrants to purchase common stock   313,440           240,000
Shares converted to common stock   590,717            
Fully diluted shares outstanding percentage   1.50%            
Series B Redeemable Convertible Preferred Stock [Member]                
Organization [Line Items]                
Common stock issued         3,092,781      
Common stock price per share         $ 4.85      
Liquidation preference value   $ 18,668,000            
Net book value   $ 18,463,000         17,897,000  
Shares converted to common stock   2,309,135       2,309,135    
Series A Redeemable Convertible Preferred Stock [Member]                
Organization [Line Items]                
Common stock issued         3,000,000      
Common stock price per share           $ 1.76    
Liquidation preference value   $ 8,598,000            
Net book value   $ 6,272,000         5,453,000  
Shares converted to common stock   2,922,798       2,922,798    
Initial Public Offering [Member]                
Organization [Line Items]                
Common stock issued   2,500,000       2,500,000    
Common stock price per share   $ 15            
Proceeds from issuance of common stock   $ 32,580,000            
Underwriting discounts, commissions and offering costs   $ 4,920,000            
Follow On Public Offering [Member]                
Organization [Line Items]                
Common stock issued 1,121,250   1,121,250          
Common stock price per share $ 23              
Underwriting discounts, commissions and offering costs $ 2,027              
Proceeds from issuance of common stock $ 23,762              
Acacia [Member]                
Organization [Line Items]                
Debt instrument principal balance           $ 0    
Warrants to purchase common stock           1,524,573    
Acacia [Member] | Bridge Loan [Member]                
Organization [Line Items]                
Common stock issued   90,000            
Debt instrument principal balance   $ 4,000,000            
Warrants to purchase common stock   120,000            
Line of credit maximum borrowing capacity   $ 8,000,000            
Shares converted to common stock   590,717            
Acacia [Member] | Initial Public Offering [Member]                
Organization [Line Items]                
Percentage of warrant exercise   10.00%            
Acacia [Member] | Convertible Notes Payable [Member]                
Organization [Line Items]                
Shares converted to common stock   1,523,746       1,523,746    
Debt instrument principal balance   $ 20,000,000         $ 20,000,000  
Accrued interest   $ 737,000            
Warrants maturity period             4 years  
Acacia [Member] | Convertible Notes Payable [Member] | Initial Public Offering [Member]                
Organization [Line Items]                
Shares converted to common stock   1,523,746            
Debt instrument principal balance   $ 20,000,000            
Accrued interest   $ 737,000            
Acacia [Member] | Convertible Notes Payable [Member] | Initial Public Offering [Member] | Bridge Loan [Member]                
Organization [Line Items]                
Shares converted to common stock   13.6088            
Debt instrument principal balance   $ 8,000,000            
Accrued interest   $ 45,000            
Acacia [Member] | Primary Warrant [Member]                
Organization [Line Items]                
Issuance of stock due to warrants exercise   2,150,335       2,150,335    
Cash proceeds from exercise of warrants   $ 29,263,000            
Warrants maturity period   5 years            
Warrants to purchase common stock   809,400            
Percentage of warrant exercise   10.00%   10.00%