Allowance for Credit Losses (Summary of Activity in the Allowance for Credit Losses by Loan Portfolio) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	$ 312,109	$ 304,031	$ 299,653	$ 379,910
Other adjustments	(105)	(65)	(139)	(2)
Charge-offs	(7,524)	(3,329)	(24,565)	(26,420)
Recoveries	4,355	3,327	9,368	11,151
Provision for credit losses	6,193	(7,909)	30,711	(68,584)
Allowance for credit losses at period end	315,028	296,055	315,028	296,055
Individually measured	10,043	10,759	10,043	10,759
Collectively measured	304,985	285,296	304,985	285,296
Loans at period end, individually measured	105,365	109,011	105,365	109,011
Loans at period end, collectively measured	37,905,355	33,124,053	37,905,355	33,124,053
Loans held at fair value	156,893	30,979	156,893	30,979
Commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	142,919	98,507	119,307	94,212
Other adjustments	0	0	0	0
Charge-offs	(780)	(1,352)	(11,122)	(16,370)
Recoveries	2,523	816	4,057	2,170
Provision for credit losses	(9,346)	11,811	23,074	29,770
Allowance for credit losses at period end	135,316	109,782	135,316	109,782
Individually measured	8,866	8,222	8,866	8,222
Collectively measured	126,450	101,560	126,450	101,560
Loans at period end, individually measured	46,547	31,001	46,547	31,001
Loans at period end, collectively measured	12,212,703	11,156,971	12,212,703	11,156,971
Loans held at fair value	0	0	0	0
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	143,732	158,522	144,583	243,603
Other adjustments	0	0	0	0
Charge-offs	(24)	(406)	(841)	(2,798)
Recoveries	55	373	640	1,087
Provision for credit losses	6,955	(18,454)	6,336	(101,857)
Allowance for credit losses at period end	150,718	140,035	150,718	140,035
Individually measured	378	1,308	378	1,308
Collectively measured	150,340	138,727	150,340	138,727
Loans at period end, individually measured	27,882	32,091	27,882	32,091
Loans at period end, collectively measured	9,550,302	8,853,623	9,550,302	8,853,623
Loans held at fair value	0	0	0	0
Home equity
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	6,990	11,207	10,699	11,437
Other adjustments	0	0	0	0
Charge-offs	(43)	(59)	(432)	(201)
Recoveries	38	313	254	742
Provision for credit losses	70	(522)	(3,466)	(1,039)
Allowance for credit losses at period end	7,055	10,939	7,055	10,939
Individually measured	71	221	71	221
Collectively measured	6,984	10,718	6,984	10,718
Loans at period end, individually measured	11,421	16,486	11,421	16,486
Loans at period end, collectively measured	317,401	331,176	317,401	331,176
Loans held at fair value	0	0	0	0
Residential real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	10,479	15,684	8,782	12,459
Other adjustments	0	0	0	0
Charge-offs	(5)	(10)	(471)	(15)
Recoveries	60	5	71	245
Provision for credit losses	489	593	2,641	3,583
Allowance for credit losses at period end	11,023	16,272	11,023	16,272
Individually measured	727	940	727	940
Collectively measured	10,296	15,332	10,296	15,332
Loans at period end, individually measured	19,440	28,966	19,440	28,966
Loans at period end, collectively measured	2,059,126	1,487,791	2,059,126	1,487,791
Loans held at fair value	156,893	30,979	156,893	30,979
Premium finance receivables
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	7,502	19,899	15,859	17,777
Other adjustments	(105)	(65)	(139)	(2)
Charge-offs	(6,037)	(1,390)	(10,618)	(6,706)
Recoveries	1,648	1,728	4,243	6,749
Provision for credit losses	7,424	(1,597)	1,087	757
Allowance for credit losses at period end	10,432	18,575	10,432	18,575
Individually measured	0	0	0	0
Collectively measured	10,432	18,575	10,432	18,575
Loans at period end, individually measured	0	0	0	0
Loans at period end, collectively measured	13,718,196	11,272,430	13,718,196	11,272,430
Loans held at fair value	0	0	0	0
Consumer and other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	487	212	423	422
Other adjustments	0	0	0	0
Charge-offs	(635)	(112)	(1,081)	(330)
Recoveries	31	92	103	158
Provision for credit losses	601	260	1,039	202
Allowance for credit losses at period end	484	452	484	452
Individually measured	1	68	1	68
Collectively measured	483	384	483	384
Loans at period end, individually measured	75	467	75	467
Loans at period end, collectively measured	47,627	22,062	47,627	22,062
Loans held at fair value	$ 0	$ 0	$ 0	$ 0