Quarterly Financial Data - Summary of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 343,773	$ 329,261	$ 327,742	$ 320,224	$ 314,594	$ 297,041	$ 280,118	$ 267,495	$ 1,321,000	$ 1,159,248	$ 834,154
Interest expense	105,232	108,636	107,508	101,576	92,541	80,241	69,366	59,897	422,952	302,045	174,107
Net interest income	238,541	220,625	220,234	218,648	222,053	216,800	210,752	207,598	898,048	857,203	660,047
Provision for credit losses	5,418	8,700	2,100	8,000	7,859	6,552	7,142	10,948	24,218	32,501	9,942
Net impairment losses on securities recognized in earnings	0	0	(2,928)	0					(2,928)	0	0
Non-interest income:
Gains on sales of loans, net	5,214	5,194	3,930	4,576	2,372	3,748	7,642	6,753	18,914	20,515	20,814
Gains (losses) on sales of assets, net	1,336	(159)	(564)	77,720	(280)	(1,899)	(125)	(97)	78,333	(2,401)	(95)
Other non-interest income	31,544	36,115	27,165	25,377	32,602	27,189	30,552	25,595
Non-interest expense:
Loss on extinguishment of debt	31,995	0	0	0					(31,995)	0	0
Amortization of tax credit investments	3,971	4,385	4,863	7,173	9,044	5,412	4,470	5,274	20,392	24,200	41,747
Other non-interest expense	160,180	141,492	136,874	140,622	144,668	146,269	145,446	168,478	63,063	69,357	46,154
Income Before Income Taxes	75,071	107,198	104,000	170,526	95,176	87,605	91,763	55,149	456,795	329,693	252,738
Income tax expense	36,967	25,307	27,532	57,196	18,074	18,046	18,961	13,184	147,002	68,265	90,831
Net Income	38,104	81,891	76,468	113,330	77,102	69,559	72,802	41,965	309,793	261,428	161,907
Dividends on preferred stock	3,172	3,172	3,172	3,172	3,172	3,172	3,172	3,172	12,688	12,688	9,449
Net Income Available to Common Shareholders	$ 34,932	$ 78,719	$ 73,296	$ 110,158	$ 73,930	$ 66,387	$ 69,630	$ 38,793	$ 297,105	$ 248,740	$ 152,458
Earnings per common share:
Basic (in usd per share)	$ 0.10	$ 0.24	$ 0.22	$ 0.33	$ 0.22	$ 0.20	$ 0.21	$ 0.12	$ 0.88	$ 0.75	$ 0.58
Diluted (in usd per share)	0.10	0.24	0.22	0.33	0.22	0.20	0.21	0.12	0.87	0.75	0.58
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	$ 0.44
Weighted average number of common shares outstanding:
Basic (in shares)	355,821,005	331,797,982	331,748,552	331,601,260	331,492,648	331,486,500	331,318,381	330,727,416	337,792,270	331,258,964	264,038,123
Diluted (in shares)	358,864,876	333,405,196	332,959,802	332,834,466	332,856,385	333,000,242	332,895,483	332,465,527	340,117,808	332,693,718	264,889,007