SELECTED QUARTERLY CONSOLIDATED FINANCIAL DATA - Selected quarterly consolidated financial data (Details) - Selected quarterly consolidated financial data - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014
Statement of Income
Interest and dividend income	$ 8,705	$ 8,650	$ 8,545	$ 8,671	$ 6,416	$ 5,444	$ 5,552	$ 5,443
Interest expense	775	753	753	745	699	690	647	668
Net interest and dividend income	7,930	7,897	7,792	7,926	5,717	4,754	4,905	4,775
(Benefit) provision for loan losses	$ 266	655	196	(200)	165	318	314	337
Gains on securities, net		6	11	175
Trust and Wealth Advisory	$ 755	798	890	822	786	791	939	779
Service charges and fees	763	798	778	731	666	$ 639	626	542
Gains on sales of mortgage loans, net	47	47	87	93	21		32	11
Mortgage servicing, net	16	5	20	(40)	15	$ 41	11	27
Other	166	115	114	115	91	82	74	79
Non-interest income	1,747	1,769	1,900	1,896	1,579	1,553	1,682	1,438
Non-interest expense	6,344	6,202	6,539	6,835	6,852	5,108	5,068	5,110
Income before income taxes	3,067	2,809	2,957	3,187	279	881	1,205	766
Income tax provision	901	824	885	953	43	113	239	215
Net income	2,166	1,985	2,072	2,234	236	768	966	551
Net income available to common shareholders	2,128	1,945	2,032	2,194	196	728	926	505
Financial Condition
Total assets	891,192	904,233	860,794	865,037	855,427	638,089	621,476	589,771
Loans, net	699,018	687,719	677,726	676,734	673,330	461,913	456,627	446,518
Allowance for loan losses	5,716	5,659	5,059	5,182	5,358	5,384	5,102	4,894
Securities	79,870	83,886	92,932	84,694	94,827	88,960	92,884	98,015
Deposits	754,533	761,479	720,734	724,910	715,426	522,294	507,361	477,512
Repurchase agreements	3,914	4,210	2,771	3,278	4,163	6,500	4,344	2,643
FHLBB advances	26,979	26,928	28,033	28,403	28,813	29,218	29,619	30,017
Shareholders' equity	90,574	105,450	104,104	103,211	101,821	75,516	75,000	74,001
Non-performing assets	$ 16,264	$ 16,602	$ 14,995	$ 14,875	$ 10,892	$ 8,945	$ 8,757	$ 8,526
Per Common Share Data
Earnings, basic and diluted					$ .10	$ .43	$ .54	$ .29
Earnings, basic	$ .78	$ .71	$ .74	$ .81
Earnings, diluted	.77	.71	.74	.80
Cash dividends declared	0.28	0.28	0.28	.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	33.13	32.72	32.26	31.96	31.54	34.74	34.44	33.90
Market price: High	33.70	31.74	32.30	30.39	28.39	30.70	30.98	27.58
Market price: Low	$ 28.80	$ 28.38	$ 28.80	$ 26.08	$ 25.88	$ 26.95	$ 27.13	$ 25.90
Statistical Data
Net interest margin (fully tax equivalent)	3.88%	3.91%	4.01%	4.11%	3.68%	3.39%	3.74%	3.72%
Efficiency ratio (fully tax equivalent)	63.64%	60.40%	62.91%	65.45%	77.80%	75.92%	72.35%	77.11%
Return on average assets	0.94%	0.87%	0.94%	1.03%	0.11%	0.45%	0.62%	0.35%
Return on average shareholders' equity	9.34%	8.64%	9.26%	10.22%	1.18%	4.85%	6.32%	3.53%
Weighted average equivalent shares outstanding, diluted					1,981	1,693	1,691	1,691
Weighted average common shares outstanding, basic	2,710	2,708	2,706	2,699
Weighted average common shares outstanding, diluted	2,727	2,724	2,724	2,716