Quarterly Financial Data - Summary of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 185,594	$ 174,690	$ 175,754	$ 170,985	$ 170,942	$ 155,459	$ 157,164	$ 153,038	$ 707,023	$ 636,603	$ 616,097
Interest expense	37,548	40,730	39,577	38,899	42,296	40,791	39,745	39,014	156,754	161,846	168,377
Net interest income	148,046	133,960	136,177	132,086	128,646	114,668	117,419	114,024	550,269	474,757	447,720
Provision for credit losses	3,507	94	4,500	0	3,980	(423)	(5,671)	3,998	8,101	1,884	16,095
Non-Interest Income
Gains (losses) on securities transactions, net	6	157	(92)	2,416	643	103	7	(8)	2,487	745	14,678
Gains on sales of loans, net	1,211	2,014	422	598	234	(95)	679	913	4,245	1,731	33,695
Gains on sales of assets, net	2,853	(558)	200	281	17,876	83	276	(148)	2,776	18,087	10,947
Other non-interest income	19,968	19,306	19,670	15,350	10,810	14,690	11,572	19,981	15,735	15,304	16,146
Non-Interest Expense
Loss on extinguishment of debt	(51,129)	0	0	0	10,132	0	0	0	51,129	10,132	0
Amortization of tax credit investments	13,081	5,224	4,511	4,496	10,048	4,630	5,802	3,716	27,312	24,196	14,352
Other	110,683	103,428	102,901	103,622	101,087	86,906	88,551	92,383	55,108	53,124	52,583
Income (loss) before income taxes	(6,316)	46,133	44,465	42,613	32,962	38,336	41,271	34,665	126,895	147,234	178,940
Income tax expense	(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
Earnings Per Common Share:
Basic (in usd per share)	$ 0.01	$ 0.15	$ 0.14	$ 0.13	$ 0.11	$ 0.14	$ 0.15	$ 0.17	$ 0.42	$ 0.56	$ 0.66
Diluted (in usd per share)	0.01	0.15	0.14	0.13	0.11	0.14	0.15	0.17	0.42	0.56	0.66
Cash dividends declared per common share (in usd per share)	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.11	$ 0.44	$ 0.44	$ 0.60
Weighted Average Number of Common Shares Outstanding:
Basic (in shares)	239,916,562	232,737,953	232,565,404	232,338,775	221,471,635	200,614,091	200,472,592	200,128,384	234,405,909	205,716,293	199,309,425
Diluted (in shares)	239,972,546	232,780,219	232,586,616	232,341,921	221,471,635	200,614,091	200,472,592	200,128,384	234,437,000	205,716,293	199,309,425