SELECTED QUARTERLY CONSOLIDATED FINANCIAL DATA - Selected quarterly consolidated financial data (Details) (Selected quarterly consolidated financial data, USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013
Selected quarterly consolidated financial data
Statement of Income
Interest and dividend income	$ 6,416	$ 5,444	$ 5,552	$ 5,443	$ 5,479	$ 5,431	$ 5,434	$ 5,406
Interest expense	699	690	647	668	686	772	801	803
Net interest and dividend income	5,717	4,754	4,905	4,775	4,793	4,659	4,633	4,603
Provision for loan losses	165	318	314	337	190	240	240	396
Trust and Wealth Advisory	786	791	939	779	775	750	824	725
Service charges and fees	666	639	626	542	612	595	575	516
Gains on sales of mortgage loans, net	21		32	11	78	69	153	279
Mortgage servicing, net	15	41	11	27	38	(37)	8	26
Other	91	82	74	79	68	82	90	79
Non-interest income	1,579	1,553	1,682	1,438	1,571	1,459	1,650	1,625
Non-interest expense	6,852	5,108	5,068	5,110	4,977	4,643	4,610	4,705
Income before income taxes	279	881	1,205	766	1,197	1,235	1,433	1,127
Income tax provision	43	113	239	215	214	219	289	187
Net income	236	768	966	551	983	1,016	1,144	940
Net income available to common shareholders	196	728	926	505	943	976	1,103	900
Financial Condition
Total assets	855,427	638,089	621,476	589,771	587,109	589,481	600,712	597,343
Loans, net	673,330	461,913	456,627	446,518	438,178	420,306	416,729	406,258
Allowance for loan losses	5,358	5,384	5,102	4,894	4,683	4,656	4,632	4,686
Securities	94,827	88,960	92,884	98,015	99,831	105,156	111,950	124,004
Deposits	715,426	522,294	507,361	477,512	477,369	479,869	492,040	487,773
Repurchase agreements	4,163	6,500	4,344	2,643	2,554	3,870	2,980	2,329
FHLBB advances	28,813	29,218	29,619	30,017	30,411	30,801	31,187	31,574
Shareholders' equity	101,821	75,516	75,000	74,001	72,790	71,211	71,489	72,206
Non-performing assets	$ 10,892	$ 8,945	$ 8,757	$ 8,526	$ 7,549	$ 9,737	$ 9,639	$ 9,297
Per Common Share Data
Earnings, basic and diluted					$ 0.55	$ 0.57	$ 0.65	$ 0.53
Earnings, basic	$ 0.10	$ 0.43	$ 0.54	$ 0.29
Earnings, diluted	$ 0.10	$ 0.43	$ 0.54	$ 0.29
Cash dividends declared	$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.28
Cash dividends paid	$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.28	$ 0.28
Book value	$ 31.54	$ 34.74	$ 34.44	$ 33.90	$ 33.21	$ 32.28	$ 32.45	$ 32.88
Market price: (a) High	$ 28.39	$ 30.70	$ 30.98	$ 27.58	$ 28.00	$ 29.95	$ 28.00	$ 26.44
Market price: (a) Low	$ 25.88	$ 26.95	$ 27.13	$ 25.90	$ 25.50	$ 25.52	$ 25.18	$ 23.55
Statistical Data
Net interest margin (fully tax equivalent)	3.68%	3.39%	3.74%	3.72%	3.71%	3.51%	3.54%	3.54%
Efficiency ratio (fully tax equivalent)	77.80%	75.92%	72.35%	77.11%	71.77%	71.72%	68.88%	70.93%
Return on average assets	0.11%	0.45%	0.62%	0.35%	0.64%	0.64%	0.74%	0.61%
Return on average shareholders' equity	1.18%	4.85%	6.32%	3.53%	6.69%	7.05%	7.81%	6.45%
Weighted average equivalent shares outstanding, diluted					1,691	1,691	1,691	1,690
Weighted average common shares outstanding, basic	1,981	1,693	1,691	1,691
Weighted average common shares outstanding, diluted	1,981	1,693	1,691	1,691