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Summary of Significant Accounting Policies - Additional Information (Detail)
1 Months Ended 3 Months Ended 12 Months Ended
Apr. 02, 2017
USD ($)
Jul. 21, 2016
Jul. 19, 2016
Jun. 13, 2016
USD ($)
Jun. 06, 2016
USD ($)
Dec. 31, 2016
USD ($)
Mar. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Segment
Sep. 30, 2017
USD ($)
Jun. 30, 2016
USD ($)
Summary Of Significant Accounting Policies [Line Items]                    
Maximum period of investments with original maturities from date of acquisition to be cash equivalents               3 months    
Reverse stock split ratio   0.0625                
Number of business segments | Segment               1    
Minimum [Member]                    
Summary Of Significant Accounting Policies [Line Items]                    
Estimated useful lives               3 years    
Reverse stock split ratio     0.1              
Maximum [Member]                    
Summary Of Significant Accounting Policies [Line Items]                    
Estimated useful lives               7 years    
Reverse stock split ratio     0.05              
Series C Warrants [Member]                    
Summary Of Significant Accounting Policies [Line Items]                    
Proceeds from issuance of notes available for general corporate purposes         $ 2,100,000          
Senior Secured Convertible Notes [Member]                    
Summary Of Significant Accounting Policies [Line Items]                    
Debt instrument, principal face amount       $ 35,000,000   $ 34,351,000   $ 34,351,000 $ 11,437,000 $ 35,000,000
Senior Secured Convertible Notes [Member] | Series C Warrants [Member]                    
Summary Of Significant Accounting Policies [Line Items]                    
Debt instrument, principal face amount                   $ 35,000,000
Senior Secured Convertible Notes [Member] | Securities Purchase Agreement [Member]                    
Summary Of Significant Accounting Policies [Line Items]                    
Debt instrument, principal face amount       35,000,000 35,000,000          
Cash proceeds from notes held       29,200,000   26,200,000   26,200,000    
Proceeds from issuance of notes available for general corporate purposes $ 3,000,000     3,000,000 3,000,000 3,000,000 $ 6,600,000      
Senior Secured Convertible Notes [Member] | Securities Purchase Agreement [Member] | Series C Warrants [Member]                    
Summary Of Significant Accounting Policies [Line Items]                    
Proceeds from issuance of notes       32,200,000 $ 32,200,000          
Senior Secured Convertible Notes [Member] | Securities Purchase Agreement [Member] | First Release Date on December 29, 2016 [Member]                    
Summary Of Significant Accounting Policies [Line Items]                    
Cash proceeds from notes held       3,000,000            
Senior Secured Convertible Notes [Member] | Securities Purchase Agreement [Member] | Subsequent Release Dates Beginning in February 2017 [Member]                    
Summary Of Significant Accounting Policies [Line Items]                    
Cash proceeds from notes held       $ 26,200,000   $ 26,200,000   $ 26,200,000