Loans and Leases (Information on How Loans and Leases were Modified as a TDR) (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) loan	Jun. 30, 2019 USD ($) loan	Jun. 30, 2020 USD ($) loan	Jun. 30, 2019 USD ($) loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	103	34	140	77
Post-Modification Recorded Investment | $	$ 21,420	$ 15,144	$ 51,659	$ 42,086
Commercial Portfolio Segment [Member] | Commercial non-mortgage | Extended Maturity [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	4	4	6	6
Post-Modification Recorded Investment | $	$ 403	$ 69	$ 507	$ 193
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	1
Post-Modification Recorded Investment | $	$ 0	$ 100	$ 0	$ 100
Commercial Portfolio Segment [Member] | Commercial non-mortgage | Maturity/Rate Combined [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	0	2	5	3
Post-Modification Recorded Investment | $	$ 0	$ 46	$ 274	$ 71
Commercial Portfolio Segment [Member] | Commercial non-mortgage | Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	13	4	23	19
Post-Modification Recorded Investment | $	$ 12,985	$ 12,029	$ 40,122	$ 34,056
Commercial Portfolio Segment [Member] | Commercial real estate | Extended Maturity [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	1	0	1	0
Post-Modification Recorded Investment | $	$ 72	$ 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	0	0	0	2
Post-Modification Recorded Investment | $	$ 0	$ 0	$ 0	$ 2,636
Consumer Portfolio Segment [Member] | Residential | Extended Maturity [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	1	3	2	4
Post-Modification Recorded Investment | $	$ 87	$ 421	$ 351	$ 940
Consumer Portfolio Segment [Member] | Residential | Maturity/Rate Combined [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	2	8	5	13
Post-Modification Recorded Investment | $	$ 255	$ 1,397	$ 698	$ 1,848
Consumer Portfolio Segment [Member] | Residential | Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	17	2	20	4
Post-Modification Recorded Investment | $	$ 3,062	$ 281	$ 3,675	$ 542
Consumer Portfolio Segment [Member] | Home equity | Extended Maturity [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	2	2	2	4
Post-Modification Recorded Investment | $	$ 157	$ 225	$ 157	$ 370
Consumer Portfolio Segment [Member] | Home equity | Maturity/Rate Combined [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	0	2	1	2
Post-Modification Recorded Investment | $	$ 0	$ 110	$ 13	$ 110
Consumer Portfolio Segment [Member] | Home equity | Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans and Leases | loan	63	6	74	19
Post-Modification Recorded Investment | $	$ 4,399	$ 466	$ 5,512	$ 1,220