FINANCIAL INSTRUMENTS WITH OFF-BALANCE SHEET RISK - Notional amounts of financial instrument with off-balance sheet credit risk (Details) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]    
Notional amounts of financial instrument with off-balance sheet credit risk $ 240,275 $ 186,959
Commitments to originate loans    
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]    
Notional amounts of financial instrument with off-balance sheet credit risk 42,625 18,641
Letters of credit    
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]    
Notional amounts of financial instrument with off-balance sheet credit risk 1,546 2,004
Unadvanced portions of loans    
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]    
Notional amounts of financial instrument with off-balance sheet credit risk $ 196,104 $ 166,314