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Redeemable Convertible Preferred Stock and Common Stock - Additional Information (Detail)
$ / shares in Units, $ in Thousands
 3 Months Ended
Mar. 31, 2018
USD ($)
Installment
$ / shares
shares
Mar. 31, 2017
USD ($)
Dec. 31, 2017
USD ($)
$ / shares
Aug. 01, 2017
$ / shares
shares
May 31, 2012
shares
Temporary Equity [Line Items]          
Accretion amount | $ $ 10 $ 10      
Common Stock          
Temporary Equity [Line Items]          
Common stock issued as payment of accrued dividends 50,799        
Shares issued during period 94,872        
Common Stock | Restricted Stock Units (RSUs)          
Temporary Equity [Line Items]          
Shares issued in connection with Employee Stock Purchase Plan and vesting of restricted stock units 44,073        
Maximum | Repricing Agreement          
Temporary Equity [Line Items]          
Limitations for issuance of common stock or voting power outstanding to holder, in percentage       19.99%  
Series A Convertible Preferred Stock          
Temporary Equity [Line Items]          
Warrants to purchase common stock         325,000
Cumulative dividends at a rate 6.00%        
Redeemable convertible preferred stock, liquidation preference per share | $ / shares $ 5.00        
Common stock issued as payment of accrued dividends 50,799        
Series A Convertible Preferred Stock | Common Stock | Repricing Agreement          
Temporary Equity [Line Items]          
Conversion price per share | $ / shares       $ 2.26  
Convertible preferred stock, shares issuable upon conversion 2,212,389        
Series A Convertible Preferred Stock | Scenario, Plan          
Temporary Equity [Line Items]          
Redeemable convertible preferred stock, liquidation preference per share | $ / shares $ 5.00        
Redemption price per share | $ / shares $ 5.00   $ 5.00    
Number of redemption price, accrued and unpaid dividends installment payments | Installment 36        
Annual interest rate on redemption value payable 6.00%        
Series A Convertible Preferred Stock | Scenario, Plan | Maximum          
Temporary Equity [Line Items]          
Majority outstanding shares redeemable date Apr. 30, 2017        
Series A Convertible Preferred Stock | Accounts Payable and Other Accrued Expenses          
Temporary Equity [Line Items]          
Total accrued but unpaid dividends | $ $ 80   $ 80    
Series A Warrants | Common Stock | Repricing Agreement          
Temporary Equity [Line Items]          
Warrants to purchase common stock       125,000  
Warrant exercise price per share | $ / shares       $ 2.72  
Series B Warrants | Common Stock | Repricing Agreement          
Temporary Equity [Line Items]          
Warrants to purchase common stock       200,000  
Warrant exercise price per share | $ / shares       $ 3.17