Income Taxes - Summary of Income Tax Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Current expense, Federal									$ 25,156	$ 13,203	$ 35,684
Current expense, State									(5,549)	3,447	2,666
Total current expense									19,607	16,650	38,350
Deferred expense (benefit), Federal and State									11,455	30,329	28,398
Income tax expense	$ 7,827	$ 10,654	$ 11,751	$ 830	$ 16,061	$ 7,143	$ 10,961	$ 12,814	$ 31,062	$ 46,979	$ 66,748