Income Taxes - Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Current income tax expense (benefit)	$ (1,152)	$ 15,224	$ 955	$ 44,636
Deferred income tax expense (benefit)	16,312	(5,332)	39,198	(9,505)
Income tax expense, as reported	$ 15,160	$ 9,892	$ 40,153	$ 35,131
Effective tax rate	11.40%	9.60%	10.70%	11.80%