Parent Company Information - Schedule of Condensed Statements of Income (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 benefit	$ (10,987)	$ 10,179	$ 12,474	$ 12,272	$ 7,827	$ 10,654	$ 11,751	$ 830	$ 23,938	$ 31,062	$ 46,979
Net Income	4,671	35,954	31,991	30,341	$ 25,135	$ 27,682	$ 29,520	$ 33,835	102,957	116,172	131,961
Dividends on preferred stock	1,796	2,017	0	0					3,813	0	0
Net Income Available to Common Shareholders	$ 2,875	$ 33,937	$ 31,991	$ 30,341					99,144	116,172	131,961
Parent Company [Member]
Dividends from subsidiary									110,000	110,000	120,000
Income from subsidiary									2,363	0	0
Other interest and income									211	436	1,477
Total Income									112,574	110,436	121,477
Total Expenses									20,578	11,172	16,140
Income before income tax benefit and equity in undistributed (losses) earnings of subsidiary									91,996	99,264	105,337
Income tax benefit									(21,939)	(3,245)	(5,130)
Income before equity in undistributed (losses) earnings of subsidiary									113,935	102,509	110,467
Equity in undistributed (losses) earnings of subsidiary									(10,978)	13,663	21,494
Net Income									102,957	116,172	131,961
Dividends on preferred stock									3,813	0	0
Net Income Available to Common Shareholders									$ 99,144	$ 116,172	$ 131,961