Business Segments - Selected Business Segment Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Business segment financial information
Net Interest Income (Loss)	$ 120,937			$ 141,655			$ 381,240	$ 399,820
Provision for Credit Losses	2,000			0			6,500	(8,000)
Net Interest Income (Loss) After Provision for Credit Losses	118,937			141,655			374,740	407,820
Noninterest Income	50,334			30,660			134,326	116,369
Noninterest Expense	(105,601)			(105,749)			(321,556)	(312,562)
Income (Loss) Before Provision for Income Taxes	63,670			66,566			187,510	211,627
Provision for Income Taxes	(15,767)			(13,765)			(46,704)	(47,130)
Net Income (Loss)	47,903	$ 46,061	$ 46,842	52,801	$ 56,862	$ 54,834	140,806	164,497
Total Assets	23,549,785			23,134,040			23,549,785	23,134,040	$ 23,606,877
Consumer Banking
Business segment financial information
Net Interest Income (Loss)	100,913			85,658			298,512	232,646
Provision for Credit Losses	1,974			1,148			6,035	3,463
Net Interest Income (Loss) After Provision for Credit Losses	98,939			84,510			292,477	229,183
Noninterest Income	31,027			30,974			94,126	94,811
Noninterest Expense	(81,377)			(83,408)			(247,543)	(247,854)
Income (Loss) Before Provision for Income Taxes	48,589			32,076			139,060	76,140
Provision for Income Taxes	(12,582)			(8,067)			(35,838)	(19,114)
Net Income (Loss)	36,007			24,009			103,222	57,026
Total Assets	8,584,221			8,399,068			8,584,221	8,399,068
Commercial Banking
Business segment financial information
Net Interest Income (Loss)	53,823			56,251			164,202	152,394
Provision for Credit Losses	74			(1)			59	(200)
Net Interest Income (Loss) After Provision for Credit Losses	53,749			56,252			164,143	152,594
Noninterest Income	8,483			(911)			25,072	17,650
Noninterest Expense	(18,937)			(17,330)			(58,528)	(53,014)
Income (Loss) Before Provision for Income Taxes	43,295			38,011			130,687	117,230
Provision for Income Taxes	(10,987)			(9,206)			(32,490)	(28,654)
Net Income (Loss)	32,308			28,805			98,197	88,576
Total Assets	5,719,577			5,486,330			5,719,577	5,486,330
Treasury and Other
Business segment financial information
Net Interest Income (Loss)	(33,799)			(254)			(81,474)	14,780
Provision for Credit Losses	(48)			(1,147)			406	(11,263)
Net Interest Income (Loss) After Provision for Credit Losses	(33,751)			893			(81,880)	26,043
Noninterest Income	10,824			597			15,128	3,908
Noninterest Expense	(5,287)			(5,011)			(15,485)	(11,694)
Income (Loss) Before Provision for Income Taxes	(28,214)			(3,521)			(82,237)	18,257
Provision for Income Taxes	7,802			3,508			21,624	638
Net Income (Loss)	(20,412)			(13)			(60,613)	18,895
Total Assets	$ 9,245,987			$ 9,248,642			$ 9,245,987	$ 9,248,642