Reportable Segments (Details) - USD ($) $ 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
Segment Reporting Information
Net interest income	$ 408,753	$ 371,793	$ 254,057	$ 254,429	$ 253,153	$ 253,502	$ 254,751	$ 247,089	$ 1,289,032	$ 1,008,495	$ 937,474
Provision for credit losses	14,403	27,188	13,569	10,122	18,894	2,270	14,236	11,368	65,282	46,768	68,443
Total noninterest income	158,052	94,258	109,718	103,504	123,868	112,064	110,151	108,314	465,532	454,397	436,063
Noninterest expense	416,571	425,620	236,849	253,075	249,958	246,423	272,039	245,980	1,332,115	1,014,400	1,059,934
Income tax expense (benefit)	21,375	(11,735)	19,314	21,287	20,013	28,034	16,418	21,631	50,241	86,096	(33,624)
Income after income tax expense (benefit)	114,456	24,978	94,043	73,449	88,156	88,839	62,209	76,424	306,926	315,628	278,784
Income attributable to non-controlling interest	2,057	2,830	3,616	2,955	2,504	2,643	3,460	2,663	11,458	11,270	10,147
Preferred stock dividends	2,494	2,494	2,494	2,493	2,494	2,494	2,494	4,106	9,975	11,588	19,904
Impact of preferred stock call	0	0	0	0	0	0	0	3,481	0	3,481	5,779
Net income available to common shareholders	109,905	$ 19,654	$ 87,933	$ 68,001	83,158	$ 83,702	$ 56,255	$ 66,174	285,493	289,289	242,954
Total assets	46,651,553				23,699,612				46,651,553	23,699,612	23,002,159
Consumer Banking
Segment Reporting Information
Net interest income									676,552	569,220	586,290
Provision for credit losses									16,550	24,661	49,683
Total noninterest income									273,915	262,797	285,222
Noninterest expense									753,904	669,967	748,272
Income tax expense (benefit)									38,353	31,645	49,927
Income after income tax expense (benefit)									141,660	105,744	23,630
Income attributable to non-controlling interest									0	0	0
Preferred stock dividends									0	0	0
Impact of preferred stock call										0	0
Net income available to common shareholders									141,660	105,744	23,630
Total assets	14,225,928				8,344,771				14,225,928	8,344,771	9,062,862
Commercial Banking
Segment Reporting Information
Net interest income									536,154	383,031	359,844
Provision for credit losses									48,732	22,107	18,760
Total noninterest income									198,898	190,442	150,526
Noninterest expense									383,390	308,727	272,888
Income tax expense (benefit)									50,581	52,675	(69,297)
Income after income tax expense (benefit)									252,349	189,964	288,019
Income attributable to non-controlling interest									11,458	11,270	10,147
Preferred stock dividends									0	0	0
Impact of preferred stock call										0	0
Net income available to common shareholders									240,891	178,694	277,872
Total assets	23,610,054				12,077,321				23,610,054	12,077,321	11,402,657
Enterprise Services
Segment Reporting Information
Net interest income									76,326	56,244	(8,660)
Provision for credit losses									0	0	0
Total noninterest income									(7,281)	1,158	315
Noninterest expense									194,821	35,706	38,774
Income tax expense (benefit)									(38,693)	1,776	(14,254)
Income after income tax expense (benefit)									(87,083)	19,920	(32,865)
Income attributable to non-controlling interest									0	0	0
Preferred stock dividends									9,975	11,588	19,904
Impact of preferred stock call										3,481	5,779
Net income available to common shareholders									(97,058)	4,851	(58,548)
Total assets	$ 8,815,571				$ 3,277,520				$ 8,815,571	$ 3,277,520	$ 2,536,640