FAIR VALUE MEASUREMENTS, Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Carrying Amount [Member] | Level 1 [Member]
Financial assets [Abstract]
Cash and cash equivalents	$ 415,628	$ 267,177
Carrying Amount [Member] | Level 2 [Member]
Financial assets [Abstract]
Certificates of deposit	13,511	16,923
Loans receivable [Abstract]
Loans held-for-sale	2,161	9,190
Interest receivable	4,743	5,099
Financial liabilities [Abstract]
Federal Home Loan Bank advances	0	5,000
Interest payable	66	59
Carrying Amount [Member] | Level 3 [Member]
Financial assets [Abstract]
Stock in Federal Home Loan Bank and other equity securities	7,097	6,480
Loans receivable [Abstract]
Net loans	823,470	875,830
Financial liabilities [Abstract]
Deposits	1,749,657	1,478,162
Fair Value [Member] | Level 1 [Member]
Financial assets [Abstract]
Cash and cash equivalents	415,628	267,177
Fair Value [Member] | Level 2 [Member]
Financial assets [Abstract]
Certificates of deposit	13,785	17,455
Loans receivable [Abstract]
Loans held-for-sale	2,198	9,522
Interest receivable	4,743	5,099
Financial liabilities [Abstract]
Federal Home Loan Bank advances	0	4,996
Interest payable	66	59
Fair Value [Member] | Level 3 [Member]
Financial assets [Abstract]
Stock in Federal Home Loan Bank and other equity securities	7,097	6,480
Loans receivable [Abstract]
Net loans	808,620	830,448
Financial liabilities [Abstract]
Deposits	$ 1,727,097	$ 1,457,051