Income Taxes - Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Current income tax expense	$ 1,361	$ 13,710	$ 2,107	$ 29,412
Deferred income tax expense (benefit)	12,475	128	22,886	(4,173)
Income tax expense, as reported	$ 13,836	$ 13,838	$ 24,993	$ 25,239
Effective tax rate	11.10%	13.90%	10.30%	12.90%