Income Taxes - Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Tax Disclosure [Abstract]
Current income tax expense	$ 16,258	$ 16,142	$ 32,088	$ 30,171
Deferred income tax expense (benefit)	(3,656)	(2,601)	(7,404)	(4,534)
Income tax expense, as reported	$ 12,602	$ 13,541	$ 24,684	$ 25,637
Effective tax rate	14.70%	16.90%	14.50%	16.70%