Loans and Leases (Information on How Loans and Leases were Modified as a TDR) (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) loan	Sep. 30, 2019 USD ($) loan	Sep. 30, 2020 USD ($) loan	Sep. 30, 2019 USD ($) loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	30	28	170	105
Post-Modification Recorded Investment | $	$ 1,958	$ 34,249	$ 53,617	$ 76,335
Commercial Portfolio Segment [Member] | Commercial non-mortgage | Extended Maturity [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	0	2	6	8
Post-Modification Recorded Investment | $	$ 0	$ 29	$ 507	$ 222
Commercial Portfolio Segment [Member] | Commercial non-mortgage | Contractual Interest Rate Reduction [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	0	1	0	2
Post-Modification Recorded Investment | $	$ 0	$ 12	$ 0	$ 112
Commercial Portfolio Segment [Member] | Commercial non-mortgage | Maturity/Rate Combined [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	2	3	7	6
Post-Modification Recorded Investment | $	$ 333	$ 225	$ 607	$ 296
Commercial Portfolio Segment [Member] | Commercial non-mortgage | Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	1	6	24	25
Post-Modification Recorded Investment | $	$ 6	$ 30,586	$ 40,128	$ 64,642
Commercial Portfolio Segment [Member] | Commercial real estate | Extended Maturity [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	0	0	1	0
Post-Modification Recorded Investment | $	$ 0	$ 0	$ 72	$ 0
Commercial Portfolio Segment [Member] | Commercial real estate | Maturity/Rate Combined [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	0	0	1	0
Post-Modification Recorded Investment | $	$ 0	$ 0	$ 278	$ 0
Commercial Portfolio Segment [Member] | Commercial real estate | Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	3	1	3	3
Post-Modification Recorded Investment | $	$ 306	$ 2,180	$ 306	$ 4,816
Consumer Portfolio Segment [Member] | Residential | Extended Maturity [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	1	1	3	5
Post-Modification Recorded Investment | $	$ 134	$ 67	$ 485	$ 1,007
Consumer Portfolio Segment [Member] | Residential | Maturity/Rate Combined [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	4	1	9	14
Post-Modification Recorded Investment | $	$ 425	$ 368	$ 1,123	$ 2,216
Consumer Portfolio Segment [Member] | Residential | Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	2	2	22	6
Post-Modification Recorded Investment | $	$ 202	$ 243	$ 3,877	$ 785
Consumer Portfolio Segment [Member] | Home equity | Extended Maturity [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	1	1	3	5
Post-Modification Recorded Investment | $	$ 31	$ 134	$ 188	$ 504
Consumer Portfolio Segment [Member] | Home equity | Maturity/Rate Combined [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	1	2	2	4
Post-Modification Recorded Investment | $	$ 15	$ 30	$ 28	$ 140
Consumer Portfolio Segment [Member] | Home equity | Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	15	8	89	27
Post-Modification Recorded Investment | $	$ 506	$ 375	$ 6,018	$ 1,595