Allowance for Credit Losses (Summary of Activity in the Allowance for Credit Losses by Loan Portfolio) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	$ 357,448	$ 299,653	$ 299,653
Other adjustments	4	22
Charge-offs	(7,351)	(4,725)
Recoveries	1,886	2,193
Provision for credit losses	23,070	4,025
Allowance for credit losses at period end	375,798	301,168	$ 357,448
Cumulative effect adjustment from the adoption of ASU 2016-13, net of tax			Accounting Standards Update 2022-02
Individually measured	12,903	5,152
Collectively measured	362,895	296,016
Loans at period end, individually evaluated for impairment	71,622	72,846
Loans at period end, collectively evaluated for impairment	39,286,317	35,149,717
Loans held-for-investment	207,532	57,984
Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	741
Allowance for credit losses at period end			$ 741
Commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	142,769	119,307	119,307
Other adjustments	0	0
Charge-offs	(2,543)	(1,414)
Recoveries	392	538
Provision for credit losses	8,772	2,480
Allowance for credit losses at period end	149,501	120,911	142,769
Individually measured	11,281	3,698
Collectively measured	138,220	117,213
Loans at period end, individually evaluated for impairment	47,950	19,651
Loans at period end, collectively evaluated for impairment	12,529,035	11,564,312
Loans held-for-investment	0	0
Commercial | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	111
Allowance for credit losses at period end			111
Commercial Real Estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	184,352	144,583	144,583
Other adjustments	0	0
Charge-offs	(5)	(777)
Recoveries	100	32
Provision for credit losses	8,977	1,068
Allowance for credit losses at period end	194,780	144,906	184,352
Individually measured	1,621	522
Collectively measured	193,159	144,384
Loans at period end, individually evaluated for impairment	11,196	22,370
Loans at period end, collectively evaluated for impairment	10,227,882	9,212,704
Loans held-for-investment	0	0
Commercial Real Estate | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	1,356
Allowance for credit losses at period end			1,356
Home  Equity
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	7,573	10,699	10,699
Other adjustments	0	0
Charge-offs	0	(197)
Recoveries	35	93
Provision for credit losses	153	(29)
Allowance for credit losses at period end	7,728	10,566	7,573
Individually measured	0	127
Collectively measured	7,728	10,439
Loans at period end, individually evaluated for impairment	1,190	12,904
Loans at period end, collectively evaluated for impairment	335,826	308,531
Loans held-for-investment	0	0
Home  Equity | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	(33)
Allowance for credit losses at period end			(33)
Residential real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	11,585	8,782	8,782
Other adjustments	0	0
Charge-offs	0	(466)
Recoveries	4	5
Provision for credit losses	537	1,108
Allowance for credit losses at period end	11,434	9,429	11,585
Individually measured	0	800
Collectively measured	11,434	8,629
Loans at period end, individually evaluated for impairment	11,280	17,842
Loans at period end, collectively evaluated for impairment	2,286,733	1,724,159
Loans held-for-investment	207,532	57,984
Residential real estate | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	(692)
Allowance for credit losses at period end			(692)
Premium Finance Receivables
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	10,671	15,859	15,859
Other adjustments	4	22
Charge-offs	(4,650)	(1,678)
Recoveries	1,323	1,476
Provision for credit losses	4,607	(957)
Allowance for credit losses at period end	11,955	14,722	10,671
Individually measured	0	0
Collectively measured	11,955	14,722
Loans at period end, individually evaluated for impairment	0	0
Loans at period end, collectively evaluated for impairment	13,864,682	12,291,571
Loans held-for-investment	0	0
Premium Finance Receivables | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	0
Allowance for credit losses at period end			0
Consumer and other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	498	423	423
Other adjustments	0	0
Charge-offs	(153)	(193)
Recoveries	32	49
Provision for credit losses	24	355
Allowance for credit losses at period end	400	634	498
Individually measured	1	5
Collectively measured	399	629
Loans at period end, individually evaluated for impairment	6	79
Loans at period end, collectively evaluated for impairment	42,159	48,440
Loans held-for-investment	0	$ 0
Consumer and other | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	$ (1)
Allowance for credit losses at period end			$ (1)