Allowance for Credit Losses (Summary of Activity in the Allowance for Credit Losses by Loan Portfolio) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	$ 301,168	$ 321,209	$ 299,653	$ 379,910
Other adjustments	(56)	33	(34)	63
Charge-offs	(12,316)	(6,975)	(17,041)	(23,091)
Recoveries	2,820	5,053	5,013	7,824
Provision for credit losses	20,493	(15,289)	24,518	(60,675)
Allowance for credit losses at period end	312,109	304,031	312,109	304,031
Individually measured	6,668	11,217	6,668	11,217
Collectively measured	305,441	292,814	305,441	292,814
Loans at period end, individually measured	85,557	113,854	85,557	113,854
Loans at period end, collectively measured	36,844,789	32,741,993	36,844,789	32,741,993
Loans held at fair value	122,757	55,340	122,757	55,340
Commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	120,911	95,640	119,307	94,212
Other adjustments	0	0	0	0
Charge-offs	(8,928)	(3,237)	(10,342)	(15,018)
Recoveries	996	902	1,534	1,354
Provision for credit losses	29,940	5,202	32,420	17,959
Allowance for credit losses at period end	142,919	98,507	142,919	98,507
Individually measured	5,674	8,625	5,674	8,625
Collectively measured	137,245	89,882	137,245	89,882
Loans at period end, individually measured	34,892	30,144	34,892	30,144
Loans at period end, collectively measured	12,012,213	11,412,132	12,012,213	11,412,132
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	144,906	181,792	144,583	243,603
Other adjustments	0	0	0	0
Charge-offs	(40)	(1,412)	(817)	(2,392)
Recoveries	553	514	585	714
Provision for credit losses	(1,687)	(22,372)	(619)	(83,403)
Allowance for credit losses at period end	143,732	158,522	143,732	158,522
Individually measured	99	1,257	99	1,257
Collectively measured	143,633	157,265	143,633	157,265
Loans at period end, individually measured	20,377	35,694	20,377	35,694
Loans at period end, collectively measured	9,386,828	8,642,675	9,386,828	8,642,675
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	10,566	11,382	10,699	11,437
Other adjustments	0	0	0	0
Charge-offs	(192)	(142)	(389)	(142)
Recoveries	123	328	216	429
Provision for credit losses	(3,507)	(361)	(3,536)	(517)
Allowance for credit losses at period end	6,990	11,207	6,990	11,207
Individually measured	105	213	105	213
Collectively measured	6,885	10,994	6,885	10,994
Loans at period end, individually measured	11,876	18,080	11,876	18,080
Loans at period end, collectively measured	313,950	351,726	313,950	351,726
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	9,429	14,242	8,782	12,459
Other adjustments	0	0	0	0
Charge-offs	0	(3)	(466)	(5)
Recoveries	6	36	11	240
Provision for credit losses	1,044	1,409	2,152	2,990
Allowance for credit losses at period end	10,479	15,684	10,479	15,684
Individually measured	790	1,045	790	1,045
Collectively measured	9,689	14,639	9,689	14,639
Loans at period end, individually measured	18,333	29,384	18,333	29,384
Loans at period end, collectively measured	1,937,817	1,445,561	1,937,817	1,445,561
Loans held at fair value	122,757	55,340	122,757	55,340
Premium finance receivables
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses at beginning of period	14,722	17,477	15,859	17,777
Other adjustments	(56)	33	(34)	63
Charge-offs	(2,903)	(2,077)	(4,581)	(5,316)
Recoveries	1,119	3,239	2,595	5,021
Provision for credit losses	(5,380)	1,227	(6,337)	2,354
Allowance for credit losses at period end	7,502	19,899	7,502	19,899
Individually measured	0	0	0	0
Collectively measured	7,502	19,899	7,502	19,899
Loans at period end, individually measured	0	0	0	0
Loans at period end, collectively measured	13,149,880	10,881,427	13,149,880	10,881,427
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	634	676	423	422
Other adjustments	0	0	0	0
Charge-offs	(253)	(104)	(446)	(218)
Recoveries	23	34	72	66
Provision for credit losses	83	(394)	438	(58)
Allowance for credit losses at period end	487	212	487	212
Individually measured	0	77	0	77
Collectively measured	487	135	487	135
Loans at period end, individually measured	79	552	79	552
Loans at period end, collectively measured	44,101	8,472	44,101	8,472
Loans held at fair value	$ 0	$ 0	$ 0	$ 0