LOANS AND ALLOWANCE FOR CREDIT LOSSES - Summary of Loans by Risk Category and Past Due Status (Details) $ in Thousands	Mar. 31, 2021 USD ($)
2021 YTD	$ 161,488
2020	698,818
2019	782,386
2018	880,631
2017	552,086
Prior	1,087,457
Revolving Loans	202,794
Total	4,365,660
Satisfactory
2021 YTD	161,488
2020	698,802
2019	780,872
2018	877,786
2017	540,266
Prior	1,051,069
Revolving Loans	200,837
Total	4,311,120
Watch
2021 YTD	0
2020	12
2019	1,364
2018	2,784
2017	11,572
Prior	28,394
Revolving Loans	714
Total	44,840
Special Mention
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving Loans	0
Total	0
Classified
2021 YTD	0
2020	4
2019	150
2018	61
2017	248
Prior	7,994
Revolving Loans	1,243
Total	9,700
Commercial Real Estate
2021 YTD	10,906
2020	130,305
2019	226,502
2018	240,367
2017	253,705
Prior	686,526
Revolving Loans	20,433
Total	1,568,744
Commercial Real Estate | Satisfactory
2021 YTD	10,906
2020	130,305
2019	226,502
2018	240,367
2017	242,150
Prior	659,242
Revolving Loans	19,838
Total	1,529,310
Commercial Real Estate | Watch
2021 YTD	0
2020	0
2019	0
2018	0
2017	11,555
Prior	21,856
Revolving Loans	595
Total	34,006
Commercial Real Estate | Special Mention
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving Loans	0
Total	0
Commercial Real Estate | Classified
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	5,428
Revolving Loans	0
Total	5,428
Consumer Loan
2021 YTD	5,822
2020	17,942
2019	13,040
2018	17,436
2017	8,743
Prior	39,566
Revolving Loans	124,915
Total	227,464
Consumer Loan | Satisfactory
2021 YTD	5,822
2020	17,926
2019	13,028
2018	17,351
2017	8,692
Prior	39,086
Revolving Loans	124,413
Total	226,318
Consumer Loan | Watch
2021 YTD	0
2020	12
2019	0
2018	24
2017	3
Prior	45
Revolving Loans	31
Total	115
Consumer Loan | Special Mention
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving Loans	0
Total	0
Consumer Loan | Classified
2021 YTD	0
2020	4
2019	12
2018	61
2017	48
Prior	435
Revolving Loans	471
Total	1,031
Construction and land development
2021 YTD	1,756
2020	22,678
2019	10,850
2018	5,110
2017	3,623
Prior	8,493
Revolving Loans	2,085
Total	54,595
Construction and land development | Satisfactory
2021 YTD	1,756
2020	22,678
2019	10,850
2018	5,110
2017	3,623
Prior	8,493
Revolving Loans	1,463
Total	53,973
Construction and land development | Watch
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving Loans	0
Total	0
Construction and land development | Special Mention
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving Loans	0
Total	0
Construction and land development | Classified
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving Loans	622
Total	622
Commercial business
2021 YTD	58,669
2020	80,786
2019	26,780
2018	27,985
2017	25,917
Prior	68,760
Revolving Loans	49,536
Total	338,433
Commercial business | Satisfactory
2021 YTD	58,669
2020	80,786
2019	26,780
2018	25,359
2017	25,903
Prior	65,918
Revolving Loans	49,485
Total	332,900
Commercial business | Watch
2021 YTD	0
2020	0
2019	0
2018	2,626
2017	14
Prior	2,775
Revolving Loans	11
Total	5,426
Commercial business | Special Mention
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving Loans	0
Total	0
Commercial business | Classified
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	67
Revolving Loans	40
Total	107
One- to four-family residential
2021 YTD	52,744
2020	206,419
2019	128,096
2018	82,479
2017	17,102
Prior	152,845
Revolving Loans	1,877
Total	641,562
One- to four-family residential | Satisfactory
2021 YTD	52,744
2020	206,419
2019	127,958
2018	82,345
2017	16,902
Prior	150,571
Revolving Loans	1,690
Total	638,629
One- to four-family residential | Watch
2021 YTD	0
2020	0
2019	0
2018	134
2017	0
Prior	228
Revolving Loans	77
Total	439
One- to four-family residential | Special Mention
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving Loans	0
Total	0
One- to four-family residential | Classified
2021 YTD	0
2020	0
2019	138
2018	0
2017	200
Prior	2,046
Revolving Loans	110
Total	2,494
One- to four-family residential construction
2021 YTD	1,938
2020	17,826
2019	2,629
2018	0
2017	0
Prior	6
Revolving Loans	230
Total	22,629
One- to four-family residential construction | Satisfactory
2021 YTD	1,938
2020	17,826
2019	1,265
2018	0
2017	0
Prior	6
Revolving Loans	230
Total	21,265
One- to four-family residential construction | Watch
2021 YTD	0
2020	0
2019	1,364
2018	0
2017	0
Prior	0
Revolving Loans	0
Total	1,364
One- to four-family residential construction | Special Mention
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving Loans	0
Total	0
One- to four-family residential construction | Classified
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving Loans	0
Total	0
Subdivision construction
2021 YTD	124
2020	1,270
2019	364
2018	302
2017	1,033
Prior	1,364
Revolving Loans	0
Total	4,457
Subdivision construction | Satisfactory
2021 YTD	124
2020	1,270
2019	364
2018	302
2017	1,033
Prior	1,346
Revolving Loans	0
Total	4,439
Subdivision construction | Watch
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving Loans	0
Total	0
Subdivision construction | Special Mention
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving Loans	0
Total	0
Subdivision construction | Classified
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	18
Revolving Loans	0
Total	18
Other Construction
2021 YTD	20,302
2020	138,048
2019	198,014
2018	117,966
2017	338
Prior	0
Revolving Loans	0
Total	474,668
Other Construction | Satisfactory
2021 YTD	20,302
2020	138,048
2019	198,014
2018	117,966
2017	338
Prior	0
Revolving Loans	0
Total	474,668
Other Construction | Watch
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving Loans	0
Total	0
Other Construction | Special Mention
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving Loans	0
Total	0
Other Construction | Classified
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving Loans	0
Total	0
Other residential
2021 YTD	9,227
2020	83,544
2019	176,111
2018	388,986
2017	241,625
Prior	129,897
Revolving Loans	3,718
Total	1,033,108
Other residential | Satisfactory
2021 YTD	9,227
2020	83,544
2019	176,111
2018	388,986
2017	241,625
Prior	126,407
Revolving Loans	3,718
Total	1,029,618
Other residential | Watch
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	3,490
Revolving Loans	0
Total	3,490
Other residential | Special Mention
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving Loans	0
Total	0
Other residential | Classified
2021 YTD	0
2020	0
2019	0
2018	0
2017	0
Prior	0
Revolving Loans	0
Total	$ 0