Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax [Line Items]
Effective tax rate	21.60%	33.70%	17.20%	29.50%
Income tax expense (benefit)	$ 53,894	$ 82,362	$ 117,255	$ 172,691
Excess tax benefit recognized	$ 12,585	$ 8,357	58,607	$ 44,720
Energy Tax Credit Carryforward
Income Tax [Line Items]
Income tax expense (benefit)			$ 6,200