DEBT SECURITIES - Amortized cost and estimated fair values of securities by contractual maturities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Available for Sale - Amortized Cost
Amortized cost, 1 year or less	$ 3,379	$ 6,203
Amortized cost, 1 year through 5 years	25,445	26,811
Amortized cost, 5 years through 10 years	10,730	9,215
Amortized cost, After 10 years	185,754	181,439
Available-for-sale Securities, Amortized Cost Basis, Total	225,308	223,668
Available for Sale - Estimated Fair Value
Estimated fair value, 1 year or less	3,355	6,194
Estimated fair value, 1 year through 5 years	25,054	26,635
Estimated fair value, 5 years through 10 years	10,768	9,348
Estimated fair value, After 10 years	181,973	180,998
Available-for-sale Securities, Total	221,150	223,175
Held to Maturity - Amortized Cost
Amortized cost, After 10 years	33	33
Held-to-maturity Securities, Total	33	33
Held to Maturity - Estimated Fair Value
Estimated fair value, After 10 years	35	35
Held-to-maturity Securities, Fair Value, Total	$ 35	$ 35