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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Jan. 01, 2017
Summary Of Significant Accounting Policies [Line Items]          
Income taxes   $ (4,493)   $ (11,519)  
Accounting Standards Update 2016-09 [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Opening deferred tax assets, valuation allowance         $ 301
Increase to the deferred tax asset balance related to the cumulative-effect adjustment         $ 301
Income taxes $ 482   $ 2,451    
Increase (decrease) in the valuation allowance $ (482)   $ (2,451)