SECURITIES - Composition of Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Amortized cost (1)
Available-for-sale
Municipal bonds	$ 4,611	$ 15,800
Mortgage-backed securities, U.S. Government agencies and U.S. Government-sponsored enterprises	49,655	53,407
Collateralized mortgage obligations, U.S. Government Agencies	10,815	1,470
Collateralized mortgage obligations, Non-agency	2,464	3,327
SBA bonds	12,767	2,056
CRA mutual funds	847	834
Corporate bonds	3,500	2,000
Preferred stock	7	7
Total securities available-for-sale	84,666	78,901
Non-marketable securities
Federal Home Loan Bank of Boston stock	3,038	3,211
Gross unrealized gains
Available-for-sale
Municipal bonds	30	197
Mortgage-backed securities, U.S. Government agencies and U.S. Government-sponsored enterprises	274	229
Collateralized mortgage obligations, U.S. Government Agencies	39	4
Collateralized mortgage obligations, Non-agency	420	414
SBA bonds	59	9
CRA mutual funds
Corporate bonds	57	16
Preferred stock	181	215
Total securities available-for-sale	1,060	1,084
Non-marketable securities
Federal Home Loan Bank of Boston stock
Gross unrealized losses
Available-for-sale
Municipal bonds		1
Mortgage-backed securities, U.S. Government agencies and U.S. Government-sponsored enterprises	172	335
Collateralized mortgage obligations, U.S. Government Agencies	13
Collateralized mortgage obligations, Non-agency	16	6
SBA bonds	10	1
CRA mutual funds	7	16
Corporate bonds		3
Preferred stock
Total securities available-for-sale	218	362
Non-marketable securities
Federal Home Loan Bank of Boston stock
Fair value
Available-for-sale
Municipal bonds	4,641	15,996
Mortgage-backed securities, U.S. Government agencies and U.S. Government-sponsored enterprises	49,757	53,301
Collateralized mortgage obligations, U.S. Government Agencies	10,841	1,474
Collateralized mortgage obligations, Non-agency	2,868	3,735
SBA bonds	12,816	2,064
CRA mutual funds	840	818
Corporate bonds	3,557	2,013
Preferred stock	188	222
Total securities available-for-sale	85,508	79,623
Non-marketable securities
Federal Home Loan Bank of Boston stock	$ 3,038	$ 3,211

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Investments in notes or bonds that are collateralized by a specific group of underlying assets owned by the issuer of the notes or bonds which are short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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The total of collateralized agreements including securities purchased under agreements to resell (repos), borrowed securities, and secured demand notes.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of securities, mortgage loans, or other financial instruments pledged as collateral for deposits.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of Federal Home Loan Bank (FHLB) and Federal Reserve Bank stock.

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For an unclassified balance sheet, this item represents investments in common and preferred stocks and other forms of securities that provide ownership interests in a corporation.

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Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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Fair value of securitized, pay-through debt securities collateralized by real estate mortgage loans classified as available-for-sale.

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Bonds or similar securities issued by state, city, or local governments or the agencies operated by state, city, or local governments which are short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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