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, 2017 USD ($) loan	Sep. 30, 2016 USD ($) loan	Sep. 30, 2017 USD ($) loan		Sep. 30, 2016 USD ($) loan
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | loan		35	38	151		133
Post-Modification Recorded Investment | $	[1]	$ 3,869	$ 10,987	$ 26,596		$ 34,367
Home Equity Loan [Member] | Adjusted Interest Rate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | loan		1	0
Post-Modification Recorded Investment | $		$ 247	$ 0
Residential Portfolio Segment [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | loan		0	4	9		11
Post-Modification Recorded Investment | $	[1]	$ 0	$ 967	$ 1,390		$ 1,969
Residential Portfolio Segment [Member] | Adjusted Interest Rate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | loan		0	1	2		2
Post-Modification Recorded Investment | $	[1]	$ 0	$ 292	$ 335		$ 528
Residential Portfolio Segment [Member] | Maturity/Rate Combined [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | loan		4	3	9		10
Post-Modification Recorded Investment | $	[1]	$ 570	$ 290	$ 1,416		$ 1,185
Residential Portfolio Segment [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | loan	[2]	6	3	32		18
Post-Modification Recorded Investment | $	[1],[2]	$ 1,357	$ 299	$ 5,471		$ 3,190
Consumer Portfolio Segment [Member] | Adjusted Interest Rate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | loan				1		0
Post-Modification Recorded Investment | $				$ 247		$ 0	[1]
Consumer Portfolio Segment [Member] | Home Equity Loan [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | loan		2	2	8		9
Post-Modification Recorded Investment | $	[1]	$ 158	$ 89	$ 822		$ 381
Consumer Portfolio Segment [Member] | Home Equity Loan [Member] | Maturity/Rate Combined [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | loan		2	3	13		11
Post-Modification Recorded Investment | $	[1]	$ 399	$ 264	$ 3,212		$ 923
Consumer Portfolio Segment [Member] | Home Equity Loan [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | loan	[2]	12	8	55		37
Post-Modification Recorded Investment | $	[1],[2]	$ 839	$ 270	$ 3,733		$ 1,447
Commercial Portfolio Segment [Member] | Commercial and Industrial Sector [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | loan		0	2	8		11
Post-Modification Recorded Investment | $	[1]	$ 0	$ 213	$ 813		$ 14,862
Commercial Portfolio Segment [Member] | Commercial and Industrial Sector [Member] | Maturity/Rate Combined [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | loan		8	0	13		2
Post-Modification Recorded Investment | $	[1]	$ 299	$ 0	$ 9,153		$ 648
Commercial Portfolio Segment [Member] | Commercial and Industrial Sector [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | loan	[2]	0	4	1		11
Post-Modification Recorded Investment | $	[1],[2]	$ 0	$ 1,265	$ 4		$ 1,639
Commercial Real Estate Portfolio Segment [Member] | Real Estate Loan [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | loan		0	1	0		1
Post-Modification Recorded Investment | $		$ 0	$ 109	$ 0	[1]	$ 109	[1]
Commercial Real Estate Portfolio Segment [Member] | Real Estate Loan [Member] | Maturity/Rate Combined [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | loan		0	1	0		2
Post-Modification Recorded Investment | $	[1]	$ 0	$ 291	$ 0		$ 335
Commercial Real Estate Portfolio Segment [Member] | Real Estate Loan [Member] | Other [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | loan	[2]	0	0	0		1
Post-Modification Recorded Investment | $	[1],[2]	$ 0	$ 0	$ 0		$ 509
Finance Leases Portfolio Segment [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | loan		0	6	0		7
Post-Modification Recorded Investment | $	[1]	$ 0	$ 6,638	$ 0		$ 6,642

[1] ost-modification balances approximate pre-modification balances. The aggregate amount of charge-offs as a result of the restructurings was not significant.

[2] ther includes covenant modifications, forbearance, loans discharged under Chapter 7 bankruptcy, or other concessions.