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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Jan. 01, 2017
Options [Member]          
Summary Of Accounting Policies [Line Items]          
Shares excluded from computations of diluted loss per share 2,014,115 1,545,512 1,968,866 627,778  
Dilutive effect of common stock equivalent shares 776,827 952,858 766,426    
ASU 2016-09 [Member]          
Summary Of Accounting Policies [Line Items]          
Cumulative-effect adjustment to retained earnings         $ 3,200