FAIR VALUE MEASUREMENTS - Assets and Liabilities Recorded at Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	$ 641,474	$ 625,074
Equity securities	11,970	11,782
Mortgage servicing rights	2,262	2,657	$ 3,472	$ 3,463
Impaired loans	901	2,509
Residential mortgage backed securities ('MBS) and collateralized mortgage obligations (CMOs)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	226,414	145,192
Commercial MBS and CMOs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	358,943	356,169
Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	56,117	123,713
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	641,474	625,074
Equity securities	11,970	11,782
Interest rate swaps		1,156
Interest rate swaps	17,674	746
Fair Value | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	0	0
Equity securities	0	0
Interest rate swaps		0
Interest rate swaps	0	0
Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	641,474	625,074
Equity securities	11,970	11,782
Interest rate swaps		1,156
Interest rate swaps	17,674	746
Fair Value | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	0	0
Equity securities	0	0
Interest rate swaps		0
Interest rate swaps	0	0
Fair Value | Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	641,474	625,074
Equity securities	11,970	11,782
Mortgage servicing rights	2,262	2,657
Interest rate swaps		1,156
Interest rate swaps	17,674	746
Fair Value | Recurring Basis | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	0	0
Equity securities	0	0
Mortgage servicing rights	0	0
Interest rate swaps		0
Interest rate swaps	0	0
Fair Value | Recurring Basis | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	641,474	625,074
Equity securities	11,970	11,782
Mortgage servicing rights	0	0
Interest rate swaps		1,156
Interest rate swaps	17,674	746
Fair Value | Recurring Basis | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	0	0
Equity securities	0	0
Mortgage servicing rights	2,262	2,657
Interest rate swaps		0
Interest rate swaps	0	0
Fair Value | Recurring Basis | Residential mortgage backed securities ('MBS) and collateralized mortgage obligations (CMOs)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	226,414	145,192
Fair Value | Recurring Basis | Residential mortgage backed securities ('MBS) and collateralized mortgage obligations (CMOs) | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	0	0
Fair Value | Recurring Basis | Residential mortgage backed securities ('MBS) and collateralized mortgage obligations (CMOs) | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	226,414	145,192
Fair Value | Recurring Basis | Residential mortgage backed securities ('MBS) and collateralized mortgage obligations (CMOs) | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	0	0
Fair Value | Recurring Basis | Commercial MBS and CMOs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	358,943	356,169
Fair Value | Recurring Basis | Commercial MBS and CMOs | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	0	0
Fair Value | Recurring Basis | Commercial MBS and CMOs | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	358,943	356,169
Fair Value | Recurring Basis | Commercial MBS and CMOs | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	0	0
Fair Value | Recurring Basis | Agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	56,117	123,713
Fair Value | Recurring Basis | Agency bonds | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	0	0
Fair Value | Recurring Basis | Agency bonds | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	56,117	123,713
Fair Value | Recurring Basis | Agency bonds | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale debt securities, at fair value	0	0
Single family residential
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	901	2,509
Single family residential | Permanent mortgages
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	1,600	1,600
Single family residential | Permanent mortgages | Nonrecurring Basis | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0	0
Single family residential | Permanent mortgages | Nonrecurring Basis | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0	0
Single family residential | Permanent mortgages | Nonrecurring Basis | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	878	790
Single family residential | Permanent mortgages | Fair Value | Nonrecurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	$ 878	$ 790