Income Taxes - Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Current income tax expense	$ 746	$ 15,702
Deferred income tax expense (benefit)	10,411	(4,301)
Income tax expense, as reported	$ 11,157	$ 11,401
Effective tax rate	9.50%	11.80%