LOANS AND ALLOWANCE FOR CREDIT LOSSES - Troubled debt restructurings ("TDRs") (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021 USD ($) contract	Dec. 31, 2020 USD ($)
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	66
Financing Receivable, Troubled Debt Restructuring	$ 3,769	$ 3,321
Construction and land development
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	1
Financing Receivable, Troubled Debt Restructuring	$ 16	20
One- to four-family residential construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	18
Financing Receivable, Troubled Debt Restructuring	$ 1,598	1,899
Commercial Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	2
Financing Receivable, Troubled Debt Restructuring	$ 1,813	646
Commercial business
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	1
Financing Receivable, Troubled Debt Restructuring	$ 52	127
Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	44
Financing Receivable, Troubled Debt Restructuring	$ 290	629
Accruing
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	40
Financing Receivable, Troubled Debt Restructuring	$ 2,587
Financing Receivable, Troubled Debt Restructuring, Accruing Interest		2,350
Accruing | Construction and land development
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	1
Financing Receivable, Troubled Debt Restructuring	$ 16
Financing Receivable, Troubled Debt Restructuring, Accruing Interest		20
Accruing | One- to four-family residential construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	8
Financing Receivable, Troubled Debt Restructuring	$ 546
Financing Receivable, Troubled Debt Restructuring, Accruing Interest		1,121
Accruing | Commercial Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	2
Financing Receivable, Troubled Debt Restructuring	$ 1,813
Financing Receivable, Troubled Debt Restructuring, Accruing Interest		646
Accruing | Commercial business
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring, Accruing Interest		52
Accruing | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	29
Financing Receivable, Troubled Debt Restructuring	$ 212
Financing Receivable, Troubled Debt Restructuring, Accruing Interest		511
Non-accruing
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	26
Financing Receivable, Troubled Debt Restructuring	$ 1,182	971
Non-accruing | One- to four-family residential construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	10
Financing Receivable, Troubled Debt Restructuring	$ 1,052	778
Non-accruing | Commercial business
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	1
Financing Receivable, Troubled Debt Restructuring	$ 52	75
Non-accruing | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts | contract	15
Financing Receivable, Troubled Debt Restructuring	$ 78	$ 118