Reportable Segments - Summary of Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information
Net interest income	$ 377,167	$ 371,793	$ 1,157,007	$ 880,279
Provision (benefit) for credit losses	69,664	27,188	245,333	50,879
Net interest income after provision for credit losses	307,503	344,605	911,674	829,400
Noninterest income	118,810	94,258	388,827	307,480
Noninterest expense	373,440	425,620	1,148,280	915,544
Income before income tax (benefit) expense	52,873	13,243	152,221	221,336
Income tax expense (benefit)	(4,429)	(11,735)	14,870	28,866
Income after income tax (benefit) expense	57,302	24,978	137,351	192,470
Income attributable to non-controlling interest	1,564	2,830	5,950	9,401
Preferred stock dividends	2,494	2,494	7,481	7,481
Net income available to common shareholders	53,244	19,654	123,920	175,588
Total assets	47,565,789	45,692,511	47,565,789	45,692,511	$ 46,651,553
Interest income	420,448	459,808	1,354,210	1,077,483
Noninterest income	118,810	94,258	388,827	307,480
Total	539,258	554,066	1,743,037	1,384,963
Consumer Banking
Segment Reporting Information
Net interest income	216,851	191,940	616,968	470,738
Provision (benefit) for credit losses	(27,217)	4,489	6,228	16,406
Net interest income after provision for credit losses	244,068	187,451	610,740	454,332
Noninterest income	78,587	57,102	245,277	183,767
Noninterest expense	204,239	210,728	640,417	520,007
Income before income tax (benefit) expense	118,416	33,825	215,600	118,092
Income tax expense (benefit)	19,744	6,817	37,478	26,529
Income after income tax (benefit) expense	98,672	27,008	178,122	91,563
Income attributable to non-controlling interest	0	0	0	0
Preferred stock dividends	0	0	0	0
Net income available to common shareholders	98,672	27,008	178,122	91,563
Total assets	13,935,521	13,701,633	13,935,521	13,701,633
Interest income	139,827	153,843	430,162	370,016
Noninterest income	78,587	57,102	245,277	183,767
Total	218,414	210,945	675,439	553,783
Commercial Banking
Segment Reporting Information
Net interest income	167,160	157,437	522,619	350,848
Provision (benefit) for credit losses	96,881	22,699	239,105	34,473
Net interest income after provision for credit losses	70,279	134,738	283,514	316,375
Noninterest income	35,105	47,929	134,709	132,883
Noninterest expense	105,646	102,841	325,425	267,147
Income before income tax (benefit) expense	(262)	79,826	92,798	182,111
Income tax expense (benefit)	(8,613)	8,172	11,133	30,271
Income after income tax (benefit) expense	8,351	71,654	81,665	151,840
Income attributable to non-controlling interest	1,564	2,830	5,950	9,401
Preferred stock dividends	0	0	0	0
Net income available to common shareholders	6,787	68,824	75,715	142,439
Total assets	23,466,019	19,045,367	23,466,019	19,045,367
Interest income	237,060	265,678	788,745	619,419
Noninterest income	35,105	47,929	134,709	132,883
Total	272,165	313,607	923,454	752,302
Enterprise Services
Segment Reporting Information
Net interest income	(6,844)	22,416	17,420	58,693
Provision (benefit) for credit losses	0	0	0	0
Net interest income after provision for credit losses	(6,844)	22,416	17,420	58,693
Noninterest income	5,118	(10,773)	8,841	(9,170)
Noninterest expense	63,555	112,051	182,438	128,390
Income before income tax (benefit) expense	(65,281)	(100,408)	(156,177)	(78,867)
Income tax expense (benefit)	(15,560)	(26,724)	(33,741)	(27,934)
Income after income tax (benefit) expense	(49,721)	(73,684)	(122,436)	(50,933)
Income attributable to non-controlling interest	0	0	0	0
Preferred stock dividends	2,494	2,494	7,481	7,481
Net income available to common shareholders	(52,215)	(76,178)	(129,917)	(58,414)
Total assets	10,164,249	12,945,511	10,164,249	12,945,511
Interest income	43,561	40,287	135,303	88,048
Noninterest income	5,118	(10,773)	8,841	(9,170)
Total	$ 48,679	$ 29,514	$ 144,144	$ 78,878