Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Estimated federal taxable income	$ 575,684	$ 471,512
Statutory federal income tax rate	35.00%
Effective tax rate	35.73%	36.52%	37.90%
Income tax expense due to reversal of previously recognized tax deductions			$ 7,000
Unrecognized tax benefits that would affect effective tax rate	$ 29,971
Accrued interest on unrecognized tax benefits		$ 125
Reversal of accrued interest on unrecognized tax benefits	1,582		$ 184
Total accrued interest on unrecognized tax benefits	19,639	$ 21,221
Reduction in unrecognized tax benefits	$ 10,614