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Cash, Cash Equivalents and Marketable Securities - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Sep. 30, 2017
Cash, cash equivalents and marketable securities [Line Items]    
Marketable securities $ 19,547 $ 0
Long-term marketable securities, minimum original maturity term 1 year  
Long-term marketable securities $ 0  
Minimum    
Cash, cash equivalents and marketable securities [Line Items]    
Short-term marketable securities, minimum original maturity term 90 days