Loans and Leases and the Allowance for Credit Losses - Loan and Leases Considered Nonaccrual and Interest Income Recognized on Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Jan. 01, 2021	Jan. 01, 2020
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	$ 945,395	$ 372,425
Amortized Cost without Allowance	1,011,711	689,323
Total	1,957,106	1,061,748
Amortized Cost			$ 1,893,299	$ 1,134,333
Interest Income Recognized	10,730	12,571
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	211,894	153,924
Amortized Cost without Allowance	83,175	132,723
Total	295,069	286,647
Amortized Cost			306,827	346,743
Interest Income Recognized	3,085	1,738
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	337,036	62,675
Amortized Cost without Allowance	487,043	125,794
Total	824,079	188,469
Amortized Cost			775,894	173,796
Interest Income Recognized	1,658	1,092
Residential Builder and Developer [Member]
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	1,224	3,204
Total	1,224	3,204
Amortized Cost			1,094	4,708
Interest Income Recognized	33	48
Other Commercial Construction [Member]
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	24,186	12,039
Amortized Cost without Allowance	102,039	22,896
Total	126,225	34,935
Amortized Cost			114,039	35,881
Interest Income Recognized	41	861
Residential [Member]
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	186,374	67,221
Amortized Cost without Allowance	199,134	226,417
Total	385,508	293,638
Amortized Cost			365,729	322,504
Interest Income Recognized	4,498	6,819
Residential Limited Documentation [Member]
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	84,342	26,444
Amortized Cost without Allowance	58,727	92,873
Total	143,069	119,317
Amortized Cost			147,170	114,667
Interest Income Recognized	79	201
Home Equity Lines and Loans [Member]
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	44,548	26,230
Amortized Cost without Allowance	34,640	36,841
Total	79,188	63,071
Amortized Cost			79,392	65,039
Interest Income Recognized	952	1,459
Recreational Finance [Member]
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	19,657	6,704
Amortized Cost without Allowance	7,561	6,701
Total	27,218	13,405
Amortized Cost			25,519	14,308
Interest Income Recognized	155	152
Automobile [Member]
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	33,270	9,802
Amortized Cost without Allowance	4,949	9,449
Total	38,219	19,251
Amortized Cost			39,404	21,293
Interest Income Recognized	49	47
Other [Member]
Financing Receivable, Impaired [Line Items]
Amortized Cost with Allowance	2,864	4,182
Amortized Cost without Allowance	34,443	35,629
Total	37,307	39,811
Amortized Cost			$ 38,231	$ 35,394
Interest Income Recognized	$ 180	$ 154