Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Estimated federal taxable income	$ 472,728	$ 391,781
Statutory federal income tax rate	35.00%
Effective tax rate	36.52%	37.90%	36.36%
Income tax expense due to reversal of previously recognized tax deductions		$ 7,000
Unrecognized tax benefits that would affect effective tax rate	$ 30,284
Accrued interest on unrecognized tax benefits	125		$ 625
Reversal of accrued interest on unrecognized tax benefits		184
Total accrued interest on unrecognized tax benefits	21,221	$ 21,096
Reduction in unrecognized tax benefits	$ 10,210