Loans (Summary of Loans) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial	$ 1,277,147		$ 1,252,419
Residential real estate	724,361		717,681
Consumer	323,537		323,903
Total loans	2,325,045	[1]	2,294,003	[1]
Percent of Total Loans	100.00%	[1]	100.00%	[1]
Loans Receivable, Deferred Income, Originated	56		39
Loans Receivable, Deferred Income, Purchased	42		83
Commercial Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral, FHLBB	230,700		238,600
Commercial Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral, FHLBB	49,800		51,800
Loans Pledged as Collateral, Federal Reserve Bank	24,700		29,500
Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral, FHLBB	631,700		627,400
Home Equity Lines [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral, FHLBB	190,100		189,400
Commercial Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial	1,277,147		1,252,419
Percent of Total Loans	55.00%		55.00%
Commercial Segment [Member] | Commercial Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial	729,968	[2]	710,813	[2]
Percent of Total Loans	31.00%	[2]	31.00%	[2]
Commercial Segment [Member] | Commercial Construction and Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial	34,179	[3]	27,842	[3]
Percent of Total Loans	2.00%	[3]	1.00%	[3]
Commercial Segment [Member] | Commercial Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial	513,000	[4]	513,764	[4]
Percent of Total Loans	22.00%	[4]	23.00%	[4]
Residential Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential real estate	724,361		717,681
Percent of Total Loans	31.00%		31.00%
Residential Segment [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential real estate	702,418	[5]	692,798	[5]
Percent of Total Loans	30.00%	[5]	30.00%	[5]
Residential Segment [Member] | Homeowner Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential real estate	21,943		24,883
Percent of Total Loans	1.00%		1.00%
Consumer Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Consumer	323,537		323,903
Percent of Total Loans	14.00%		14.00%
Consumer Segment [Member] | Home Equity Lines [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Consumer	226,640	[6]	226,861	[6]
Percent of Total Loans	10.00%	[6]	10.00%	[6]
Consumer Segment [Member] | Home Equity Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Consumer	40,134	[6]	39,329	[6]
Percent of Total Loans	2.00%	[6]	2.00%	[6]
Consumer Segment [Member] | Other Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Consumer	$ 56,763	[7]	$ 57,713	[7]
Percent of Total Loans	2.00%	[7]	2.00%	[7]

[1] Includes net unamortized loan origination costs of $56 thousand and $39 thousand, respectively, and net unamortized premiums on purchased loans of $42 thousand and $83 thousand, respectively, at March 31, 2013 and December 31, 2012.

[2] Amortizing mortgages and lines of credit, primarily secured by income producing property. As of March 31, 2013 and December 31, 2012, $230.7 million and $238.6 million, respectively, were pledged as collateral for FHLBB borrowings.

[3] Loans for construction of residential and commercial properties and for land development.

[4] Loans to businesses and individuals, a substantial portion of which are fully or partially collateralized by real estate. As of March 31, 2013, $49.8 million and $24.7 million, respectively, were pledged as collateral for FHLBB borrowings and were collateralized for the discount window at the Federal Reserve Bank. Comparable amounts for December 31, 2012 were $51.8 million and $29.5 million, respectively.

[5] As of March 31, 2013 and December 31, 2012, $631.7 million and $627.4 million, respectively, were pledged as collateral for FHLBB borrowings.

[6] As of March 31, 2013 and December 31, 2012, $190.1 million and $189.4 million, respectively, were pledged as collateral for FHLBB borrowings.

[7] Fixed-rate consumer installment loans.