Reportable Segments - Summary of Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Segment Reporting Information
Net interest income	$ 381,827	$ 401,481
Provision (benefit) for credit losses	20,556	96,943
Net interest income after provision for credit losses	361,271	304,538
Noninterest income	132,060	136,963
Noninterest expense	348,682	374,599
Income before income tax expense	144,649	66,902
Income tax expense (benefit)	19,540	13,086
Income after income tax expense	125,109	53,816
Income attributable to non-controlling interest	1,773	1,917
Preferred stock dividends	2,493	2,493
Net income available to common shareholders	120,843	49,406
Total assets	49,459,551	48,594,383	$ 47,802,487
Consumer Banking
Segment Reporting Information
Net interest income	199,374	193,832
Provision (benefit) for credit losses	4,101	44,369
Net interest income after provision for credit losses	195,273	149,463
Noninterest income	81,390	81,414
Noninterest expense	212,304	228,859
Income before income tax expense	64,359	2,018
Income tax expense (benefit)	13,401	1,982
Income after income tax expense	50,958	36
Income attributable to non-controlling interest	0	0
Preferred stock dividends	0	0
Net income available to common shareholders	50,958	36
Total assets	13,699,477	14,463,055
Commercial Banking
Segment Reporting Information
Net interest income	174,018	185,986
Provision (benefit) for credit losses	16,455	52,574
Net interest income after provision for credit losses	157,563	133,412
Noninterest income	49,016	55,773
Noninterest expense	110,630	114,455
Income before income tax expense	95,949	74,730
Income tax expense (benefit)	19,568	16,306
Income after income tax expense	76,381	58,424
Income attributable to non-controlling interest	1,773	1,917
Preferred stock dividends	0	0
Net income available to common shareholders	74,608	56,507
Total assets	25,941,038	24,859,839
Enterprise Services
Segment Reporting Information
Net interest income	8,435	21,663
Provision (benefit) for credit losses	0	0
Net interest income after provision for credit losses	8,435	21,663
Noninterest income	1,654	(224)
Noninterest expense	25,748	31,285
Income before income tax expense	(15,659)	(9,846)
Income tax expense (benefit)	(13,429)	(5,202)
Income after income tax expense	(2,230)	(4,644)
Income attributable to non-controlling interest	0	0
Preferred stock dividends	2,493	2,493
Net income available to common shareholders	(4,723)	(7,137)
Total assets	$ 9,819,036	$ 9,271,489