Business Segments - Schedule of Financial Data for Business Segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Average interest earning assets (unaudited)	$ 37,010,933	$ 30,575,530	$ 27,702,911
Interest income	1,383,719	1,321,000	1,159,248
Interest expense	264,815	422,952	302,045
Net Interest Income	1,118,904	898,048	857,203
Provision for credit losses	125,722	24,218	32,501
Net Interest Income After Provision for Credit Losses	993,182	873,830	824,702
Non-interest income	183,032	214,520	134,052
Non-interest expense	646,148	631,555	629,061
Internal transfer expense (income)	0	0	0
Income Before Income Taxes	$ 530,066	$ 456,795	$ 329,693
Return on average interest earning assets (pre-tax) (unaudited)	1.43%	1.49%	1.19%
Corporate and Other Adjustments
Segment Reporting Information [Line Items]
Average interest earning assets (unaudited)	$ 0	$ 0	$ 0
Interest income	(4,156)	(4,824)	(5,961)
Interest expense	18,214	15,669	15,577
Net Interest Income	(22,370)	(20,493)	(21,538)
Provision for credit losses	0	0	0
Net Interest Income After Provision for Credit Losses	(22,370)	(20,493)	(21,538)
Non-interest income	26,667	106,564	41,806
Non-interest expense	468,720	452,551	440,177
Internal transfer expense (income)	(402,211)	(349,526)	(344,916)
Income Before Income Taxes	(62,212)	(16,954)	(74,993)
Consumer Lending | Operating Segments
Segment Reporting Information [Line Items]
Average interest earning assets (unaudited)	7,160,793	6,891,462	6,197,161
Interest income	257,196	272,773	235,264
Interest expense	47,712	91,798	64,083
Net Interest Income	209,484	180,975	171,181
Provision for credit losses	11,502	6,688	5,550
Net Interest Income After Provision for Credit Losses	197,982	174,287	165,631
Non-interest income	81,499	57,981	61,280
Non-interest expense	77,582	76,046	92,462
Internal transfer expense (income)	77,835	78,743	77,164
Income Before Income Taxes	$ 124,064	$ 77,479	$ 57,285
Return on average interest earning assets (pre-tax) (unaudited)	1.73%	1.12%	0.92%
Commercial Lending | Operating Segments
Segment Reporting Information [Line Items]
Average interest earning assets (unaudited)	$ 24,625,066	$ 19,343,791	$ 17,143,169
Interest income	1,027,796	926,328	798,974
Interest expense	164,075	257,670	177,273
Net Interest Income	863,721	668,658	621,701
Provision for credit losses	113,585	17,530	26,951
Net Interest Income After Provision for Credit Losses	750,136	651,128	594,750
Non-interest income	64,783	41,157	22,275
Non-interest expense	98,710	101,924	95,171
Internal transfer expense (income)	267,588	221,113	213,399
Income Before Income Taxes	$ 448,621	$ 369,248	$ 308,455
Return on average interest earning assets (pre-tax) (unaudited)	1.82%	1.91%	1.80%
Investment Management | Operating Segments
Segment Reporting Information [Line Items]
Average interest earning assets (unaudited)	$ 5,225,074	$ 4,340,277	$ 4,362,581
Interest income	102,883	126,723	130,971
Interest expense	34,814	57,815	45,112
Net Interest Income	68,069	68,908	85,859
Provision for credit losses	635	0	0
Net Interest Income After Provision for Credit Losses	67,434	68,908	85,859
Non-interest income	10,083	8,818	8,691
Non-interest expense	1,136	1,034	1,251
Internal transfer expense (income)	56,788	49,670	54,353
Income Before Income Taxes	$ 19,593	$ 27,022	$ 38,946
Return on average interest earning assets (pre-tax) (unaudited)	0.37%	0.62%	0.89%