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Financings - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Nov. 11, 2018
May 11, 2017
Dec. 31, 2018
Dec. 31, 2017
Apr. 26, 2006
Class of Stock [Line Items]          
Stock issued during period   9,708,738      
Issuance & sale of common stock in public offering price per share   $ 5.15      
Sale of stock price per share   $ 4.893      
Net proceeds from issuance of common stock   $ 47,300      
Common stock, par value $ 0.001   $ 0.001 $ 0.001 $ 0.001
Gross proceeds received     $ 47,101 $ 47,270  
Securities Purchase Agreement [Member]          
Class of Stock [Line Items]          
Stock issued during period 18,939,394        
Common stock, par value $ 0.001        
par value per share $ 2.64        
Gross proceeds received $ 47,100