Income Taxes - Summary of Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Current expense, Federal									$ 7,978	$ 25,156	$ 13,203
Current expense, State									(493)	(5,549)	3,447
Total current expense									7,485	19,607	16,650
Deferred expense (benefit), Federal and State									16,453	11,455	30,329
Income tax expense	$ (10,987)	$ 10,179	$ 12,474	$ 12,272	$ 7,827	$ 10,654	$ 11,751	$ 830	$ 23,938	$ 31,062	$ 46,979