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FAIR VALUE MEASUREMENTS - Assets and Liabilities Recorded at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Financial assets:
Available for sale debt securities, at fair value	$ 635,324		$ 625,074
Equity securities	12,070		11,782
Mortgage servicing rights	2,028	$ 2,262	2,657	$ 3,155	$ 3,472	$ 3,463
Financial liabilities:
Impaired loans	894		2,509
With no related allowance recorded	5,282		5,129
Residential MBS
Financial assets:
Available for sale debt securities, at fair value	261,617		145,192
Commercial MBS and CMOs
Financial assets:
Available for sale debt securities, at fair value	358,011		356,169
Agency bonds
Financial assets:
Available for sale debt securities, at fair value	15,696		123,713
Fair Value
Financial assets:
Available for sale debt securities, at fair value	635,324		625,074
Equity securities	12,070		11,782
Interest rate swaps			1,156
Financial liabilities:
Interest rate swaps	14,723		746
Fair Value \| Level 1
Financial assets:
Available for sale debt securities, at fair value	0		0
Equity securities	0		0
Interest rate swaps			0
Financial liabilities:
Interest rate swaps	0		0
Fair Value \| Level 2
Financial assets:
Available for sale debt securities, at fair value	635,324		625,074
Equity securities	12,070		11,782
Interest rate swaps			1,156
Financial liabilities:
Interest rate swaps	14,723		746
Fair Value \| Level 3
Financial assets:
Available for sale debt securities, at fair value	0		0
Equity securities	0		0
Interest rate swaps			0
Financial liabilities:
Interest rate swaps	0		0
Fair Value \| Recurring Basis
Financial assets:
Available for sale debt securities, at fair value	635,324		625,074
Equity securities	12,070		11,782
Mortgage servicing rights	2,028		2,657
Interest rate swaps			1,156
Financial liabilities:
Interest rate swaps	14,723		746
Fair Value \| Recurring Basis \| Level 1
Financial assets:
Available for sale debt securities, at fair value	0		0
Equity securities	0		0
Mortgage servicing rights	0		0
Interest rate swaps			0
Financial liabilities:
Interest rate swaps	0		0
Fair Value \| Recurring Basis \| Level 2
Financial assets:
Available for sale debt securities, at fair value	635,324		625,074
Equity securities	12,070		11,782
Mortgage servicing rights	0		0
Interest rate swaps			1,156
Financial liabilities:
Interest rate swaps	14,723		746
Fair Value \| Recurring Basis \| Level 3
Financial assets:
Available for sale debt securities, at fair value	0		0
Equity securities	0		0
Mortgage servicing rights	2,028		2,657
Interest rate swaps			0
Financial liabilities:
Interest rate swaps	0		0
Fair Value \| Recurring Basis \| Residential MBS
Financial assets:
Available for sale debt securities, at fair value	261,617		145,192
Fair Value \| Recurring Basis \| Residential MBS \| Level 1
Financial assets:
Available for sale debt securities, at fair value	0		0
Fair Value \| Recurring Basis \| Residential MBS \| Level 2
Financial assets:
Available for sale debt securities, at fair value	261,617		145,192
Fair Value \| Recurring Basis \| Residential MBS \| Level 3
Financial assets:
Available for sale debt securities, at fair value	0		0
Fair Value \| Recurring Basis \| Commercial MBS and CMOs
Financial assets:
Available for sale debt securities, at fair value	358,011		356,169
Fair Value \| Recurring Basis \| Commercial MBS and CMOs \| Level 1
Financial assets:
Available for sale debt securities, at fair value	0		0
Fair Value \| Recurring Basis \| Commercial MBS and CMOs \| Level 2
Financial assets:
Available for sale debt securities, at fair value	358,011		356,169
Fair Value \| Recurring Basis \| Commercial MBS and CMOs \| Level 3
Financial assets:
Available for sale debt securities, at fair value	0		0
Fair Value \| Recurring Basis \| Agency bonds
Financial assets:
Available for sale debt securities, at fair value	15,696		123,713
Fair Value \| Recurring Basis \| Agency bonds \| Level 1
Financial assets:
Available for sale debt securities, at fair value	0		0
Fair Value \| Recurring Basis \| Agency bonds \| Level 2
Financial assets:
Available for sale debt securities, at fair value	15,696		123,713
Fair Value \| Recurring Basis \| Agency bonds \| Level 3
Financial assets:
Available for sale debt securities, at fair value	0		0
Single family residential
Financial liabilities:
Impaired loans	894		2,509
With no related allowance recorded	4,749		4,588
Single family residential \| Permanent mortgages
Financial liabilities:
Impaired loans			1,600
With no related allowance recorded	1,600
Single family residential \| Permanent mortgages \| Nonrecurring Basis \| Level 1
Financial liabilities:
Impaired loans			0
With no related allowance recorded	0
Single family residential \| Permanent mortgages \| Nonrecurring Basis \| Level 2
Financial liabilities:
Impaired loans			0
With no related allowance recorded	0
Single family residential \| Permanent mortgages \| Nonrecurring Basis \| Level 3
Financial liabilities:
Impaired loans			790
With no related allowance recorded	878
Single family residential \| Permanent mortgages \| Fair Value \| Nonrecurring Basis
Financial liabilities:
Impaired loans			$ 790
With no related allowance recorded	$ 878