Loans and Leases and the Allowance for Credit Losses - Loan Modification Activities that were Considered Troubled Debt Restructurings (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($) Modification	Mar. 31, 2020 USD ($) Modification
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	855	96
Pre-modification Recorded Investment	$ 131,632	$ 66,502
post modification recorded investment	129,961	66,517
Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment	85,516	13,019
Other [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment	2,214
Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment	$ 42,231	$ 53,498
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	93	32
Pre-modification Recorded Investment	$ 53,733	$ 12,692
post modification recorded investment	53,157	12,053
Commercial, Financial, Leasing, etc. [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment	24,653	5,066
Commercial, Financial, Leasing, etc. [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment	$ 28,504	$ 6,987
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	33	10
Pre-modification Recorded Investment	$ 26,870	$ 39,642
post modification recorded investment	25,796	37,323
Commercial Real Estate [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment	11,160	1,355
Commercial Real Estate [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment	2,214
Commercial Real Estate [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment	$ 12,422	$ 35,968
Residential [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	123	27
Pre-modification Recorded Investment	$ 39,583	$ 10,178
post modification recorded investment	39,674	12,224
Residential [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment	38,557	3,247
Residential [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment	$ 1,117	$ 8,977
Home Equity Lines and Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	26	6
Pre-modification Recorded Investment	$ 1,715	$ 738
post modification recorded investment	1,660	746
Home Equity Lines and Loans [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment	1,486	412
Home Equity Lines and Loans [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment	$ 174	$ 334
Recreational Finance [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	72	3
Pre-modification Recorded Investment	$ 2,212	$ 90
post modification recorded investment	2,212	90
Recreational Finance [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment	$ 2,212	$ 90
Automobile [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	276	9
Pre-modification Recorded Investment	$ 4,969	$ 182
post modification recorded investment	4,969	182
Automobile [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment	4,955	$ 182
Automobile [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment	$ 14
Other [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	222
Pre-modification Recorded Investment	$ 1,434
post modification recorded investment	1,434
Other [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment	$ 1,434
Residential Limited Documentation [Member]
Financing Receivable, Modifications [Line Items]
Number of modifications | Modification	10	9
Pre-modification Recorded Investment	$ 1,116	$ 2,980
post modification recorded investment	1,059	3,899
Residential Limited Documentation [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment	$ 1,059	2,667
Residential Limited Documentation [Member] | Combination of Concession Types [Member]
Financing Receivable, Modifications [Line Items]
post modification recorded investment		$ 1,232