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General - Additional Information (Detail)
 3 Months Ended 9 Months Ended 12 Months Ended
Nov. 06, 2017
$ / shares
shares
Jul. 21, 2016
$ / shares
shares
Sep. 30, 2017
USD ($)
$ / shares
Sep. 30, 2016
USD ($)
Sep. 30, 2017
USD ($)
$ / shares
Sep. 30, 2016
USD ($)
Dec. 31, 2016
USD ($)
$ / shares
Dec. 31, 2015
USD ($)
$ / shares
Jun. 30, 2016
USD ($)
Jun. 13, 2016
USD ($)
Class Of Stock [Line Items]                    
Reverse stock split ratio   0.0625                
Number of fractional shares were issued in connection with the reverse stock split | shares   0                
Common stock, par value (in dollars per share) | $ / shares   $ 0.01 $ 0.01   $ 0.01   $ 0.01 $ 0.01    
Net loss     $ 12,596,000 $ 1,004,000 $ 25,873,000 $ 9,485,000 $ 17,971,000 $ 14,704,000    
Net cash used in operating activities         11,659,000 $ 10,597,000 14,213,000 16,420,000    
Accumulated deficit     305,587,000   305,587,000   279,188,000 $ 261,217,000    
Senior Secured Convertible Notes [Member]                    
Class Of Stock [Line Items]                    
Debt instrument, principal face amount     $ 11,437,000   $ 11,437,000   $ 34,351,000   $ 35,000,000 $ 35,000,000
Subsequent Event [Member]                    
Class Of Stock [Line Items]                    
Reverse stock split ratio 0.0029                  
Subsequent Event [Member] | OTCQB [Member]                    
Class Of Stock [Line Items]                    
Reverse stock split ratio 0.0029                  
Number of fractional shares were issued in connection with the reverse stock split | shares 0                  
Common stock, par value (in dollars per share) | $ / shares $ 0.01