COMMITMENTS AND CONTINGENCIES - Loan commitments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Loan commitments
Commitments to grant loans	$ 16,298	$ 4,254
Home equity loans and lines of credit
Loan commitments
Unadvanced funds on loan	8,513	8,809
Commercial lines of credit
Loan commitments
Unadvanced funds on loan	14,713	12,324
Construction loans:
Loan commitments
Unadvanced funds on loan	12,423	8,943
Other unsecured personal lines of credit
Loan commitments
Unadvanced funds on loan	287	411
Commercial real estate
Loan commitments
Unadvanced funds on loan	5,618	8,143
Standby letters of credit
Loan commitments
Standby letters of credit	$ 62	$ 85
Standby letters of credit | Maximum
Loan commitments
Term of letters of credit	1 year