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Stockholders' Equity - Additional Information (Detail) - USD ($)
 12 Months Ended 22 Months Ended
Mar. 15, 2018
Feb. 15, 2018
Feb. 13, 2018
Dec. 22, 2017
Dec. 20, 2017
Apr. 12, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2017
Mar. 16, 2016
Stockholders Equity Disclosure [Line Items]                    
Common stock, value of shares issued under sales agreement             $ 6,000 $ 1,000 $ 6,000  
Net proceeds from sale of common stock       $ 9,700,000   $ 18,600,000 $ 5,336,000 $ 958,000    
Warrants to purchase common stock           2,070,000        
Warrants exercise price           $ 5.50   $ 145.11    
Preferred stock, shares issued             3,680 0 3,680  
Preferred stock, shares outstanding             3,680 0 3,680  
Net proceeds allocated to common stock, preferred A stock and warrants             $ 18,563,000      
Common stock price, per share           $ 5.28        
Proceeds allocated to warrants, net           $ 5,000,000        
Subsequent Event                    
Stockholders Equity Disclosure [Line Items]                    
Net proceeds from sale of common stock   $ 106,700,000                
Preferred stock, shares outstanding 0                  
Overallotment Option                    
Stockholders Equity Disclosure [Line Items]                    
Warrants to purchase common stock           270,000        
Series A Preferred Stock                    
Stockholders Equity Disclosure [Line Items]                    
Issuance of stock, shares           13,350        
Conversion of each preferred stock to common stock           200        
Number of shares converted             9,670      
Preferred stock, shares issued             3,680   3,680  
Preferred stock, shares outstanding             3,680   3,680  
Net proceeds allocated to preferred stock             $ 10,100,000      
Effective conversion price             $ 3.80   $ 3.80  
Intrinsic value of preferred stock           $ 4,000,000        
Effective percentage of conversion rights           100.00%        
Common Stock                    
Stockholders Equity Disclosure [Line Items]                    
Issuance of stock, shares       1,105,263   1,470,000 439,880 39,743    
Conversion of preferred stock to common stock             1,934,000 8    
Common stock price, per share       $ 9.50            
Firm commitment underwritten public offering shares         1,105,263          
Common Stock | Subsequent Event                    
Stockholders Equity Disclosure [Line Items]                    
Issuance of stock, shares   3,382,352                
Conversion of preferred stock to common stock 716,000                  
Common stock price, per share   $ 34.00                
Firm commitment underwritten public offering shares     2,941,176              
Common Stock | Overallotment Option                    
Stockholders Equity Disclosure [Line Items]                    
Issuance of stock, shares           540,000        
Common Stock | Overallotment Option | Subsequent Event                    
Stockholders Equity Disclosure [Line Items]                    
Issuance of stock, shares   441,176                
Capital on Demand Sales Agreement with Jones Trading Institutional Services LLC                    
Stockholders Equity Disclosure [Line Items]                    
Issuance of stock, shares                 479,681  
Common stock weighted average selling price                 $ 13.55  
Net proceeds from sale of common stock             $ 5,500,000   $ 6,300,000  
Commission against additional paid-in capital                 $ 200,000  
Common stock available for sale             0   0  
Capital on Demand Sales Agreement with Jones Trading Institutional Services LLC | Maximum                    
Stockholders Equity Disclosure [Line Items]                    
Common stock, value of shares issued under sales agreement                   $ 6,500,000