Loans and Leases and the Allowance for Credit Losses - Summary of Outstanding Loan Balances Related to COVID-19 Modifications Granted (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		$ 124,785	$ 73,598	$ 507,582	$ 283,415
Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		56,116	35,178	196,378	117,336
COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount				2,416,803
COVID-19 [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[1]			2,115,790
COVID-19 [Member] | Other Forbearances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[2]			301,013
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		49,772	34,955	173,377	101,678
Commercial, Financial, Leasing, etc. [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		6,051	7,145	42,143	29,762
Commercial, Financial, Leasing, etc. [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount				53,876
Commercial, Financial, Leasing, etc. [Member] | COVID-19 [Member] | Other Forbearances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[2]			53,876
Commercial [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount				225,807
Commercial [Member] | COVID-19 [Member] | Other Forbearances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[2]			225,807
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount				532
Other Commercial Construction [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount				532
Other Commercial Construction [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount				21,330
Other Commercial Construction [Member] | COVID-19 [Member] | Other Forbearances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[2]			21,330
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		14,265	9,133	87,802	30,991
Residential [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		12,281	5,517	80,411	11,865
Residential [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount				1,925,639
Residential [Member] | COVID-19 [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[1],[3]			1,925,639
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		828		2,292	3,899
Residential Limited Documentation [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		828		2,292	2,667
Residential Limited Documentation [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount				177,200
Residential Limited Documentation [Member] | COVID-19 [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[1]			177,200
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		1,349	3,415	4,979	11,745
Home Equity Lines and Loans [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		1,246	129	4,702	688
Home Equity Lines and Loans [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount				6,188
Home Equity Lines and Loans [Member] | COVID-19 [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[1]			6,188
Recreational Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		2,565	2,734	5,896	13,619
Recreational Finance [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		2,565	2,734	5,896	13,619
Recreational Finance [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount				2,252
Recreational Finance [Member] | COVID-19 [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[1]			2,252
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		2,711	7,007	9,182	33,541
Automobile [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		2,711	$ 7,005	9,168	$ 33,539
Automobile [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount				4,314
Automobile [Member] | COVID-19 [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[1]			4,314
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		123		2,393
Other [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		$ 123		2,393
Other [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount				197
Other [Member] | COVID-19 [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[1]			$ 197

[1] Represents accruing loans at September 30, 2021 for which a COVID-19 related payment deferral (including maturity extensions) has been granted

[2] Consists predominantly of accruing loans for which a COVID-19 related covenant waiver has been granted

[3] Includes $1.6 billion of government-guaranteed loans