Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Tax [Line Items]
Effective tax rate	13.10%	22.10%
Income tax expense (benefit)	$ 24,949	$ 29,238
Excess tax benefit recognized	19,567	$ 19,900
Energy Tax Credit Carryforward
Income Tax [Line Items]
Income tax expense (benefit)	$ 6,200