Loans and Leases - Summary of Outstanding Loan Balances Related to COVID-19 Modifications Granted (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		$ 806,046	$ 127,024	$ 180,224
Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		545,415	29,481	90,639
COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		4,579,759
COVID-19 [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[1]	3,767,523
COVID-19 [Member] | Other Forbearances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[2]	812,236
Commercial, Financial, Leasing, etc. [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		199,918	63,356	102,914
Commercial, Financial, Leasing, etc. [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		70,671	10,485	50,490
Commercial, Financial, Leasing, etc. [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		387,780
Commercial, Financial, Leasing, etc. [Member] | COVID-19 [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[1]	95,823
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]	291,957
Commercial [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		1,103,020
Commercial [Member] | COVID-19 [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[1]	728,511
Commercial [Member] | COVID-19 [Member] | Other Forbearances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[2]	374,509
Residential Builder and Developer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		90	1,068
Residential Builder and Developer [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount			1,068
Residential Builder and Developer [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		653
Residential Builder and Developer [Member] | COVID-19 [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[1]	653
Other Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		13,573	1,500	746
Other Commercial Construction [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		13,573		746
Other Commercial Construction [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		207,005
Other Commercial Construction [Member] | COVID-19 [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[1]	61,235
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]	145,770
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		207,517	22,726	38,072
Residential [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		183,878	10,819	19,962
Residential [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		2,447,422
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]	2,447,422
Residential Limited Documentation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		8,332	1,443	2,250
Residential Limited Documentation [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		7,100	399	827
Residential Limited Documentation [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		337,108
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]	337,108
Home Equity Lines and Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		17,254	4,180	3,979
Home Equity Lines and Loans [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		5,882	176	224
Home Equity Lines and Loans [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		18,440
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]	18,440
Recreational Finance [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		16,392	265	202
Recreational Finance [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		16,388	265	202
Recreational Finance [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		24,428
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]	24,428
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		39,951	1,141	1,330
Automobile [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		39,949	$ 1,076	$ 1,318
Automobile [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		51,550
Automobile [Member] | COVID-19 [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[1]	51,550
Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		7,788
Other [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		3,383
Other [Member] | COVID-19 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount		2,353
Other [Member] | COVID-19 [Member] | Payment Deferral [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, net of unearned discount	[1]	$ 2,353

[1] Represents accruing loans at December 31, 2020 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 $1.7 billion of government-guaranteed loans.