Income Taxes - Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Current income tax expense	$ 15,224	$ 12,848	$ 44,636	$ 40,251
Deferred income tax expense (benefit)	(5,332)	(1,996)	(9,505)	(11,629)
Income tax expense, as reported	$ 9,892	$ 10,852	$ 35,131	$ 28,622
Effective tax rate	9.60%	11.90%	11.80%	11.50%