SELECTED QUARTERLY CONSOLIDATED FINANCIAL DATA - Selected quarterly consolidated financial data (Details) (USD $)	3 Months Ended				12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statement of Income
Interest and dividend income	$ 5,426,000	$ 5,607,000	$ 5,766,000	$ 5,858,000
Interest expense	992,000	1,035,000	1,080,000	1,175,000
Net interest and dividend income	4,434,000	4,572,000	4,686,000	4,683,000
Provision for loan losses	380,000	330,000	180,000	180,000
Trust and Wealth Advisory	772,000	683,000	735,000	755,000	2,945,000	2,548,000	2,102,000
Service charges and fees	561,000	559,000	547,000	521,000
Gains on sales of mortgage loans, net	394,000	568,000	263,000	372,000
Mortgage servicing, net	76,000	(9,000)	(5,000)	(84,000)
Securities gains			267,000	12,000
Other	74,000	86,000	83,000	83,000
Non-interest income	1,877,000	1,887,000	1,890,000	1,659,000
Non-interest expense	5,334,000	4,693,000	5,026,000	4,500,000	19,554,000	17,639,000	17,113,000
Income before income taxes	597,000	1,436,000	1,370,000	1,662,000
Income tax provision	26,000	296,000	254,000	412,000
Net income	571,000	1,140,000	1,116,000	1,250,000
Net income available to common shareholders	531,000	1,094,000	1,069,000	1,167,000
Total assets	600,813,000	611,037,000	600,857,000	598,950,000
Loans, net	388,758,000	377,377,000	377,212,000	371,709,000
Allowance for loan losses	4,360,000	4,179,000	4,208,000	4,166,000
Securities	132,034,000	131,412,000	141,409,000	151,666,000
Deposits	491,215,000	490,206,000	477,910,000	472,686,000
Repurchase agreements	1,784,000	2,941,000	6,181,000	10,359,000
FHLBB advances	31,980,000	42,392,000	42,801,000	43,207,000
Shareholders' equity	71,997,000	70,374,000	69,126,000	68,067,000
Non-performing assets	10,104,000	9,870,000	8,409,000	7,606,000
Per Common Share Data
Earnings, diluted and basic	$ 0.31	$ 0.65	$ 0.63	$ 0.69
Cash dividends declared	280	280	280	280
Cash dividends paid	$ 280	$ 280	$ 280	$ 280
Book value	$ 33.14	$ 32.18	$ 31.44	$ 30.83
Market price
High	$ 28.47	$ 26.39	$ 26.49	$ 26.95
Low	$ 23.16	$ 23.11	$ 23.25	$ 22.51
Statistical Data
Net interest margin (fully tax equivalent)	3.32%	3.39%	3.58%	3.54%
Efficiency ratio (fully tax equivalent)	$ 71.45	$ 66.05	$ 66.39	$ 66.86
Return on average assets	$ 0.35	$ 0.71	$ 0.72	$ 0.78
Return on average shareholders' equity	$ 3.85	$ 8.05	$ 8.10	$ 9.05
Weighted average equivalent shares outstanding, diluted	1,690	1,690	1,689	1,689