Income Taxes - Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Tax Disclosure [Abstract]
Current income tax expense	$ 13,710	$ 13,616	$ 29,412	$ 27,403
Deferred income tax expense (benefit)	128	(5,238)	(4,173)	(9,633)
Income tax expense, as reported	$ 13,838	$ 8,378	$ 25,239	$ 17,770
Effective tax rate	13.90%	10.50%	12.90%	11.20%