FAIR VALUE MEASUREMENTS - Carrying value and estimated fair values of financial instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Carrying value
Financial Assets
Cash and cash equivalents	$ 48,486	$ 35,485
Securities available-for-sale	79,047	79,623
Federal Home Loan Bank stock	3,813	3,211
Loans held-for-sale	669
Loans receivable, net	801,703	763,184
Accrued interest receivable	2,665	2,424
Cash surrender value of life insurance	14,381	14,038
Financial Liabilities
Demand (non-interest-bearing)	220,536	218,420
Demand (interest-bearing)	142,575	127,854
Money market	190,953	182,476
Savings and other	144,600	135,435
Certificates of deposit	116,831	117,585
Deposits	815,495	781,770
Repurchase agreements	1,668	5,535
FHLBB advances	54,422	37,188
Subordinated debt	9,811	9,788
Note payable	313	344
Capital lease liability	1,835	418
Accrued interest payable	99	89
Estimated fair value
Financial Assets
Cash and cash equivalents	48,486	35,485
Securities available-for-sale	79,047	79,623
Federal Home Loan Bank stock	3,813	3,211
Loans held-for-sale	669
Loans receivable, net	816,451	774,442
Accrued interest receivable	2,665	2,424
Cash surrender value of life insurance	14,381	14,038
Financial Liabilities
Demand (non-interest-bearing)	220,536	218,420
Demand (interest-bearing)	142,575	127,854
Money market	190,953	182,476
Savings and other	144,600	135,435
Certificates of deposit	115,290	118,610
Deposits	813,954	782,795
Repurchase agreements	1,668	5,535
FHLBB advances	54,918	38,440
Subordinated debt	10,313	10,378
Note payable	341	377
Capital lease liability	2,161	841
Accrued interest payable	99	89
Fair Value Measurements Using - Level 1
Financial Assets
Cash and cash equivalents	48,486	35,485
Securities available-for-sale	835	1,040
Federal Home Loan Bank stock
Loans held-for-sale
Loans receivable, net
Accrued interest receivable
Cash surrender value of life insurance	14,381	14,038
Financial Liabilities
Demand (non-interest-bearing)
Demand (interest-bearing)
Money market
Savings and other
Certificates of deposit
Deposits
Repurchase agreements
FHLBB advances
Subordinated debt
Note payable
Capital lease liability
Accrued interest payable
Fair Value Measurements Using - Level 2
Financial Assets
Cash and cash equivalents
Securities available-for-sale	78,212	78,583
Federal Home Loan Bank stock		3,211
Loans held-for-sale
Loans receivable, net
Accrued interest receivable
Cash surrender value of life insurance
Financial Liabilities
Demand (non-interest-bearing)
Demand (interest-bearing)
Money market
Savings and other
Certificates of deposit
Deposits
Repurchase agreements
FHLBB advances
Subordinated debt
Note payable
Capital lease liability
Accrued interest payable
Fair Value Measurements Using - Level 3
Financial Assets
Cash and cash equivalents
Securities available-for-sale
Federal Home Loan Bank stock	3,813
Loans held-for-sale	669
Loans receivable, net	816,451	774,442
Accrued interest receivable	2,665	2,424
Cash surrender value of life insurance
Financial Liabilities
Demand (non-interest-bearing)	220,536	218,420
Demand (interest-bearing)	142,575	127,854
Money market	190,953	182,476
Savings and other	144,600	135,435
Certificates of deposit	115,290	118,610
Deposits	813,954	782,795
Repurchase agreements	1,668	5,535
FHLBB advances	54,918	38,440
Subordinated debt	10,313	10,378
Note payable	341	377
Capital lease liability	2,161	841
Accrued interest payable	$ 99	$ 89