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Income Taxes - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Investments, Owned, Federal Income Tax Note [Line Items]        
Effective income tax rate reconciliation at federal statutory income tax rate     33.40% 35.90%
Income Tax Expense (Benefit) $ 13,160 $ 19,197 $ 21,593 $ 35,365
U.S. Federal        
Investments, Owned, Federal Income Tax Note [Line Items]        
Effective income tax rate reconciliation at federal statutory income tax rate     35.00%