Loans and Credit Quality (Troubled Debt Restructured Loans Outstanding) (Detail) - USD ($) $ in Thousands		Mar. 31, 2017	Dec. 31, 2016
Performing Financial Instruments [Member]
Troubled Debt Restructured Loans Outstanding [Line Items]
Troubled debt restructured loans outstanding		$ 87,908	$ 66,002
Performing Financial Instruments [Member] | Commercial Portfolio Segment [Member]
Troubled Debt Restructured Loans Outstanding [Line Items]
Troubled debt restructured loans outstanding		85,974	63,711
Performing Financial Instruments [Member] | Commercial Real Estate Portfolio Segment [Member]
Troubled Debt Restructured Loans Outstanding [Line Items]
Troubled debt restructured loans outstanding		0	0
Performing Financial Instruments [Member] | Residential Real Estate Portfolio Segment [Member]
Troubled Debt Restructured Loans Outstanding [Line Items]
Troubled debt restructured loans outstanding		0	0
Performing Financial Instruments [Member] | Home Equity Loan Portfolio Segment [Member]
Troubled Debt Restructured Loans Outstanding [Line Items]
Troubled debt restructured loans outstanding		1,934	2,291
Nonperforming Financial Instruments [Member]
Troubled Debt Restructured Loans Outstanding [Line Items]
Troubled debt restructured loans outstanding	[1]	41,727	43,613
Nonperforming Financial Instruments [Member] | Commercial Portfolio Segment [Member]
Troubled Debt Restructured Loans Outstanding [Line Items]
Troubled debt restructured loans outstanding	[1]	32,795	33,141
Nonperforming Financial Instruments [Member] | Commercial Real Estate Portfolio Segment [Member]
Troubled Debt Restructured Loans Outstanding [Line Items]
Troubled debt restructured loans outstanding	[1]	5,101	5,857
Nonperforming Financial Instruments [Member] | Residential Real Estate Portfolio Segment [Member]
Troubled Debt Restructured Loans Outstanding [Line Items]
Troubled debt restructured loans outstanding	[1]	1,227	1,534
Nonperforming Financial Instruments [Member] | Home Equity Loan Portfolio Segment [Member]
Troubled Debt Restructured Loans Outstanding [Line Items]
Troubled debt restructured loans outstanding	[1]	$ 2,604	$ 3,081

[1] Included in nonperforming loans.