Parent Company Information - Schedule of Condensed Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Income Statements, Captions [Line Items]
Gains (losses) on securities transactions, net									$ 777	$ 2,487	$ 745
Income tax benefit	$ 18,336	$ 17,049	$ 15,460	$ 14,389	$ (10,987)	$ 10,179	$ 12,474	$ 12,272	65,234	23,938	31,062
Net Income	50,090	42,842	39,027	36,187	4,671	35,954	31,991	30,341	168,146	102,957	116,172
Dividends on preferred stock	1,797	1,797	1,797	1,797	1,796	2,017	0	0	7,188	3,813	0
Net Income Available to Common Shareholders	$ 48,293	$ 41,045	$ 37,230	$ 34,390	$ 2,875	$ 33,937	$ 31,991	$ 30,341	160,958	99,144	116,172
Parent Company
Condensed Income Statements, Captions [Line Items]
Dividends from subsidiary									90,000	110,000	110,000
Income from subsidiary									4,550	2,363	0
Gains (losses) on securities transactions, net									239	0	0
Other interest and income									34	211	436
Total Income									94,823	112,574	110,436
Total Expenses									33,604	20,578	11,172
Income before income tax benefit and equity in undistributed (losses) earnings of subsidiary									61,219	91,996	99,264
Income tax benefit									(23,349)	(21,939)	(3,245)
Income before equity in undistributed earnings (losses) of subsidiary									84,568	113,935	102,509
Equity in undistributed earnings (losses) of subsidiary									83,578	(10,978)	13,663
Net Income									168,146	102,957	116,172
Dividends on preferred stock									7,188	3,813	0
Net Income Available to Common Shareholders									$ 160,958	$ 99,144	$ 116,172