Loans (Summary of Loans) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial	$ 1,252,419		$ 1,124,628
Residential real estate	717,681		700,414
Consumer	323,903		322,117
Total loans	2,294,003	[1]	2,147,159	[1]
Percent of total loans	100.00%	[1]	100.00%	[1]
Loans pledged as collateral, FHLBB	1,100,000		911,500
Net unamortized loan origination costs	39		31
Net unamortized premiums on purchased loans	83		67
Commercial Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral, FHLBB	238,600		107,100
Commercial Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral, FHLBB	51,800		27,200
Loans pledged as collateral, Federal Reserve Bank	29,500		42,100
Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral, FHLBB	627,400		611,800
Home Equity Lines [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral, FHLBB	189,400		165,400
Commercial Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial	1,252,419		1,124,628
Percent of total loans	55.00%		52.00%
Commercial Segment [Member] | Commercial Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial	710,813	[2]	624,813	[2]
Percent of total loans	31.00%	[2]	29.00%	[2]
Commercial Segment [Member] | Commercial Construction and Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial	27,842	[3]	10,955	[3]
Percent of total loans	1.00%	[3]	1.00%	[3]
Commercial Segment [Member] | Commercial Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial	513,764	[4]	488,860	[4]
Percent of total loans	23.00%	[4]	22.00%	[4]
Residential Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential real estate	717,681		700,414
Percent of total loans	31.00%		33.00%
Residential Segment [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential real estate	692,798	[5]	678,582	[5]
Percent of total loans	30.00%	[5]	32.00%	[5]
Residential Segment [Member] | Homeowner Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential real estate	24,883		21,832
Percent of total loans	1.00%		1.00%
Consumer Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Consumer	323,903		322,117
Percent of total loans	14.00%		15.00%
Consumer Segment [Member] | Home Equity Lines [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Consumer	226,861	[6]	223,430	[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	39,329	[6]	43,121	[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	$ 57,713	[7]	$ 55,566	[7]
Percent of total loans	2.00%	[7]	3.00%	[7]

[1] Includes net unamortized loan origination costs of $39 thousand and $31 thousand, respectively, and net unamortized premiums on purchased loans of $83 thousand and $67 thousand, respectively, at December 31, 2012 and 2011.

[2] Amortizing mortgages and lines of credit, primarily secured by income producing property. As of December 31, 2012 and 2011, $238.6 million and $107.1 million, respectively, of these loans were pledged as collateral for FHLBB borrowings (see Note 11).

[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 December 31, 2012, $51.8 million and $29.5 million, respectively, of these loans were pledged as collateral for FHLBB borrowings and were collateralized for the discount window at the Federal Reserve Bank. Comparable amounts for December 31, 2011 were $27.2 million and $42.1 million, respectively (see Note 11).

[5] As of December 31, 2012 and 2011, $627.4 million and $611.8 million, respectively, of these loans were pledged as collateral for FHLBB borrowings (see Note 11).

[6] As of December 31, 2012 and 2011, $189.4 million and $165.4 million, respectively, of these loans were pledged as collateral for FHLBB borrowings (see Note 11).

[7] Fixed rate consumer installment loans.