Income Taxes - Summary of Income Tax Expense Allocated Based on Separate Tax Return Basis (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Current income taxes: Federal taxes	$ 69,572	$ 18,111	$ 33,614
Current income taxes: State taxes	989	396	(116)
Current income taxes	70,561	18,507	33,498
Deferred income taxes: Federal taxes	63	44,113	11,258
Deferred income taxes: State taxes	(631)
Deferred income taxes	(568)	44,113	11,258
Income taxes	$ 69,993	$ 62,620	$ 44,756