Allowance for Credit Losses - Schedule of Activity in the Allowance for Credit Losses by Loan Portfolio (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	$ 387,380	$ 312,109	$ 357,448	$ 299,653	$ 299,653
Other adjustments	(60)	(105)	(15)	(139)
Charge-offs	(10,477)	(7,524)	(36,344)	(24,565)
Recoveries	2,359	4,355	5,731	9,368
Provision for credit losses	19,948	6,193	71,589	30,711
Allowance for credit losses at period end	399,150	315,028	399,150	315,028	$ 357,448
Individually measured	15,302	10,043	15,302	10,043
Collectively measured	383,848	304,985	383,848	304,985
Loans at period end, individually evaluated for impairment	77,937	105,365	77,937	105,365
Loans at period end, collectively evaluated for impairment	41,196,917	37,905,355	41,196,917	37,905,355
Loans held-for-investment	171,178	156,893	171,178	156,893
Accounting Standards Update 2016-13
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Cumulative effect adjustment from the adoption of ASU 2016-13, net of tax					Accounting Standards Update 2016-13
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	143,142	142,919	142,769	119,307	119,307
Other adjustments	0	0	0	0
Charge-offs	(2,427)	(780)	(10,599)	(11,122)
Recoveries	1,162	2,523	2,059	4,057
Provision for credit losses	9,611	(9,346)	17,148	23,074
Allowance for credit losses at period end	151,488	135,316	151,488	135,316	142,769
Individually measured	9,773	8,866	9,773	8,866
Collectively measured	141,715	126,450	141,715	126,450
Loans at period end, individually evaluated for impairment	43,569	46,547	43,569	46,547
Loans at period end, collectively evaluated for impairment	12,681,904	12,212,703	12,681,904	12,212,703
Loans held-for-investment	0	0	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	215,696	143,732	184,352	144,583	144,583
Other adjustments	0	0	0	0
Charge-offs	(1,713)	(24)	(9,842)	(841)
Recoveries	243	55	368	640
Provision for credit losses	1,492	6,955	39,484	6,336
Allowance for credit losses at period end	215,718	150,718	215,718	150,718	184,352
Individually measured	5,408	378	5,408	378
Collectively measured	210,310	150,340	210,310	150,340
Loans at period end, individually evaluated for impairment	17,043	27,882	17,043	27,882
Loans at period end, collectively evaluated for impairment	10,929,137	9,550,302	10,929,137	9,550,302
Loans held-for-investment	0	0	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	6,967	6,990	7,573	10,699	10,699
Other adjustments	0	0	0	0
Charge-offs	(227)	(43)	(227)	(432)
Recoveries	33	38	105	254
Provision for credit losses	307	70	(338)	(3,466)
Allowance for credit losses at period end	7,080	7,055	7,080	7,055	7,573
Individually measured	0	71	0	71
Collectively measured	7,080	6,984	7,080	6,984
Loans at period end, individually evaluated for impairment	1,363	11,421	1,363	11,421
Loans at period end, collectively evaluated for impairment	341,895	317,401	341,895	317,401
Loans held-for-investment	0	0	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	12,252	10,479	11,585	8,782	8,782
Other adjustments	0	0	0	0
Charge-offs	(78)	(5)	(78)	(471)
Recoveries	1	60	11	71
Provision for credit losses	484	489	1,833	2,641
Allowance for credit losses at period end	12,659	11,023	12,659	11,023	11,585
Individually measured	109	727	109	727
Collectively measured	12,550	10,296	12,550	10,296
Loans at period end, individually evaluated for impairment	15,946	19,440	15,946	19,440
Loans at period end, collectively evaluated for impairment	2,520,479	2,059,126	2,520,479	2,059,126
Loans held-for-investment	171,178	156,893	171,178	156,893
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	9,046	7,502	10,671	15,859	15,859
Other adjustments	(60)	(105)	(15)	(139)
Charge-offs	(5,848)	(6,037)	(15,151)	(10,618)
Recoveries	906	1,648	3,119	4,243
Provision for credit losses	7,776	7,424	13,196	1,087
Allowance for credit losses at period end	11,820	10,432	11,820	10,432	10,671
Individually measured	0	0	0	0
Collectively measured	11,820	10,432	11,820	10,432
Loans at period end, individually evaluated for impairment	0	0	0	0
Loans at period end, collectively evaluated for impairment	14,654,555	13,718,196	14,654,555	13,718,196
Loans held-for-investment	0	0	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	277	487	498	423	423
Other adjustments	0	0	0	0
Charge-offs	(184)	(635)	(447)	(1,081)
Recoveries	14	31	69	103
Provision for credit losses	278	601	266	1,039
Allowance for credit losses at period end	385	484	385	484	498
Individually measured	12	1	12	1
Collectively measured	373	483	373	483
Loans at period end, individually evaluated for impairment	16	75	16	75
Loans at period end, collectively evaluated for impairment	68,947	47,627	68,947	47,627
Loans held-for-investment	$ 0	$ 0	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)