Income Taxes (Income Tax Expense) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Current income tax expense	$ 58,707	$ 48,748	$ 59,530
Deferred income tax expense (benefit)	(14,493)	(11,598)	(19,059)
Income tax expense, as reported	$ 44,214	$ 37,150	$ 40,471
Effective tax rate	10.80%	10.90%	12.70%