Quarterly Financial Data - Summary of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 314,594	$ 297,041	$ 280,118	$ 267,495	$ 217,951	$ 210,741	$ 207,007	$ 198,455	$ 1,159,248	$ 834,154	$ 761,888
Interest expense	92,541	80,241	69,366	59,897	48,537	46,796	42,187	36,587	302,045	174,107	148,774
Net interest income	222,053	216,800	210,752	207,598	169,414	163,945	164,820	161,868	857,203	660,047	613,114
Provision for credit losses	7,859	6,552	7,142	10,948	2,200	1,640	3,632	2,470	32,501	9,942	11,869
Non-interest income:
Gains on sales of loans, net	2,372	3,748	7,642	6,753	6,375	5,520	4,791	4,128	20,515	20,814	22,030
Other non-interest income	32,322	25,290	30,427	25,498	23,784	21,477	24,039	21,592	43,206	24,967	21,988
Non-interest expense:
Amortization of tax credit investments	9,044	5,412	4,470	5,274	20,302	8,389	7,732	5,324	24,200	41,747	34,744
Other non-interest expense	144,668	146,269	145,446	168,478	116,015	124,176	111,507	115,628	69,357	46,154	51,816
Income Before Income Taxes	95,176	87,605	91,763	55,149	61,056	56,737	70,779	64,166	329,693	252,738	233,380
Income tax expense	18,074	18,046	18,961	13,184	34,958	17,088	20,714	18,071	68,265	90,831	65,234
Net Income	77,102	69,559	72,802	41,965	26,098	39,649	50,065	46,095	261,428	161,907	168,146
Dividends on preferred stock	3,172	3,172	3,172	3,172	3,172	2,683	1,797	1,797	12,688	9,449	7,188
Net Income Available to Common Shareholders	$ 73,930	$ 66,387	$ 69,630	$ 38,793	$ 22,926	$ 36,966	$ 48,268	$ 44,298	$ 248,740	$ 152,458	$ 160,958
Earnings per common share:
Basic (in usd per share)	$ 0.22	$ 0.20	$ 0.21	$ 0.12	$ 0.09	$ 0.14	$ 0.18	$ 0.17	$ 0.75	$ 0.58	$ 0.63
Diluted (in usd per share)	0.22	0.20	0.21	0.12	0.09	0.14	0.18	0.17	0.75	0.58	0.63
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)	331,492,648	331,486,500	331,318,381	330,727,416	264,332,895	264,058,174	263,958,292	263,797,024	331,258,964	264,038,123	254,841,571
Diluted (in shares)	332,856,385	333,000,242	332,895,483	332,465,527	265,288,067	264,936,220	264,778,242	264,546,266	332,693,718	264,889,007	255,268,336