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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
Schedule Of Significant Accounting Policies [Line Items]        
Income tax expense (benefit) $ 6,635 $ 17,281 $ 41,354 $ 54,400
Adjustments for New Accounting Pronouncement [Member]        
Schedule Of Significant Accounting Policies [Line Items]        
Income tax expense (benefit)     $ (800)