Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Tax [Line Items]
Effective tax rate	15.90%	29.20%	14.60%	26.50%
Income tax expense (benefit)	$ 38,412	$ 61,091	$ 63,361	$ 90,329
Excess tax benefit recognized	$ 26,456	$ 16,464	46,022	$ 36,364
Energy Tax Credit Carryforward
Income Tax [Line Items]
Income tax expense (benefit)			$ 6,200