LOANS AND ALLOWANCE FOR CREDIT LOSSES - Schedule of Loans Classified by Aging Analysis (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financial Asset, 30 to 59 Days Past Due | Commercial Real Estate
Financing Receivables, By Class	$ 302
Financial Asset, 30 to 59 Days Past Due | Industrial revenue bonds
Financing Receivables, By Class	944
Financial Asset, 30 to 59 Days Past Due | Consumer auto
Financing Receivables, By Class	145	$ 364
Financial Asset, 30 to 59 Days Past Due | Home Equity Line of Credit
Financing Receivables, By Class	40	153
Financial Asset, 30 to 59 Days Past Due | Land development
Financing Receivables, By Class	14	20
Financial Asset, 30 to 59 Days Past Due | One- to four-family residential construction
Financing Receivables, By Class	249	1,365
Financial Asset, 30 to 59 Days Past Due | Owner occupied one- to four-family residential
Financing Receivables, By Class	2,017	1,379
Financial Asset, 30 to 59 Days Past Due | Commercial business
Financing Receivables, By Class	83
Financial Asset, 30 to 59 Days Past Due | Consumer
Financing Receivables, By Class	117	443
Financial Asset, 30 to 59 Days Past Due | Acquired Loans Net of Discount
Financing Receivables, By Class		1,662
Financial Asset, 30 to 59 Days Past Due | Less Acquired Loans Net of Discount
Financing Receivables, By Class	2,133	1,662
Financial Asset, 30 to 59 Days Past Due | Loans Receivable, Gross
Financing Receivables, By Class	3,911	5,386
Financial Asset, 30 to 59 Days Past Due | Loans Receivable
Financing Receivables, By Class	1,778	3,724
Financial Asset, 60 to 89 Days Past Due | Commercial Real Estate
Financing Receivables, By Class		79
Financial Asset, 60 to 89 Days Past Due | Consumer auto
Financing Receivables, By Class	30	119
Financial Asset, 60 to 89 Days Past Due | Home Equity Line of Credit
Financing Receivables, By Class	63	111
Financial Asset, 60 to 89 Days Past Due | Owner occupied one- to four-family residential
Financing Receivables, By Class	252	113
Financial Asset, 60 to 89 Days Past Due | Consumer
Financing Receivables, By Class	25	7
Financial Asset, 60 to 89 Days Past Due | Acquired Loans Net of Discount
Financing Receivables, By Class		641
Financial Asset, 60 to 89 Days Past Due | Less Acquired Loans Net of Discount
Financing Receivables, By Class	109	641
Financial Asset, 60 to 89 Days Past Due | Loans Receivable, Gross
Financing Receivables, By Class	370	1,070
Financial Asset, 60 to 89 Days Past Due | Loans Receivable
Financing Receivables, By Class	261	429
Financial Asset, Equal to or Greater than 90 Days Past Due | Commercial Real Estate
Financing Receivables, By Class	3,394	587
Financial Asset, Equal to or Greater than 90 Days Past Due | Consumer auto
Financing Receivables, By Class	106	169
Financial Asset, Equal to or Greater than 90 Days Past Due | Home Equity Line of Credit
Financing Receivables, By Class	810	508
Financial Asset, Equal to or Greater than 90 Days Past Due | Land development
Financing Receivables, By Class	622
Financial Asset, Equal to or Greater than 90 Days Past Due | Owner occupied one- to four-family residential
Financing Receivables, By Class	4,111	1,502
Financial Asset, Equal to or Greater than 90 Days Past Due | Non-owner occupied one- to four-family residential
Financing Receivables, By Class	112	69
Financial Asset, Equal to or Greater than 90 Days Past Due | Other residential
Financing Receivables, By Class	185
Financial Asset, Equal to or Greater than 90 Days Past Due | Commercial business
Financing Receivables, By Class	106	114
Financial Asset, Equal to or Greater than 90 Days Past Due | Consumer
Financing Receivables, By Class	100	94
Financial Asset, Equal to or Greater than 90 Days Past Due | Acquired Loans Net of Discount
Financing Receivables, By Class		3,843
Financial Asset, Equal to or Greater than 90 Days Past Due | Less Acquired Loans Net of Discount
Financing Receivables, By Class	3,576	3,843
Financial Asset, Equal to or Greater than 90 Days Past Due | Loans Receivable, Gross
Financing Receivables, By Class	9,546	6,886
Financial Asset, Equal to or Greater than 90 Days Past Due | Loans Receivable
Financing Receivables, By Class	5,970	3,043
Financing Receivables Past Due | Commercial Real Estate
Financing Receivables, By Class	3,696	666
Financing Receivables Past Due | Industrial revenue bonds
Financing Receivables, By Class	944
Financing Receivables Past Due | Consumer auto
Financing Receivables, By Class	281	652
Financing Receivables Past Due | Home Equity Line of Credit
Financing Receivables, By Class	913	772
Financing Receivables Past Due | Land development
Financing Receivables, By Class	636	20
Financing Receivables Past Due | One- to four-family residential construction
Financing Receivables, By Class	249	1,365
Financing Receivables Past Due | Owner occupied one- to four-family residential
Financing Receivables, By Class	6,380	2,994
Financing Receivables Past Due | Non-owner occupied one- to four-family residential
Financing Receivables, By Class	112	69
Financing Receivables Past Due | Other residential
Financing Receivables, By Class	185
Financing Receivables Past Due | Commercial business
Financing Receivables, By Class	189	114
Financing Receivables Past Due | Consumer
Financing Receivables, By Class	242	544
Financing Receivables Past Due | Acquired Loans Net of Discount
Financing Receivables, By Class		6,146
Financing Receivables Past Due | Less Acquired Loans Net of Discount
Financing Receivables, By Class	5,818	6,146
Financing Receivables Past Due | Loans Receivable, Gross
Financing Receivables, By Class	13,827	13,342
Financing Receivables Past Due | Loans Receivable
Financing Receivables, By Class	8,009	7,196
Financing Receivables Current | Commercial construction
Financing Receivables, By Class	1,206,687	1,212,837
Financing Receivables Current | Commercial Real Estate
Financing Receivables, By Class	1,585,075	1,553,011
Financing Receivables Current | Industrial revenue bonds
Financing Receivables, By Class	13,615	14,003
Financing Receivables Current | Consumer auto
Financing Receivables, By Class	73,370	85,521
Financing Receivables Current | Home Equity Line of Credit
Financing Receivables, By Class	112,881	113,917
Financing Receivables Current | Land development
Financing Receivables, By Class	53,954	53,990
Financing Receivables Current | One- to four-family residential construction
Financing Receivables, By Class	47,912	41,428
Financing Receivables Current | Subdivision construction
Financing Receivables, By Class	7,297	30,894
Financing Receivables Current | Owner occupied one- to four-family residential
Financing Receivables, By Class	503,963	467,442
Financing Receivables Current | Non-owner occupied one- to four-family residential
Financing Receivables, By Class	130,497	114,500
Financing Receivables Current | Other residential
Financing Receivables, By Class	1,055,210	1,021,145
Financing Receivables Current | Commercial business
Financing Receivables, By Class	372,344	370,784
Financing Receivables Current | Consumer
Financing Receivables, By Class	39,482	40,218
Financing Receivables Current | Acquired Loans Net of Discount
Financing Receivables, By Class		92,497
Financing Receivables Current | Less Acquired Loans Net of Discount
Financing Receivables, By Class	86,116	92,497
Financing Receivables Current | Loans Receivable, Gross
Financing Receivables, By Class	5,202,287	5,212,187
Financing Receivables Current | Loans Receivable
Financing Receivables, By Class	5,116,171	5,119,690
Financing Receivables Total | Commercial construction
Financing Receivables, By Class	1,206,687	1,212,837
Financing Receivables Total | Commercial Real Estate
Financing Receivables, By Class	1,588,771	1,553,677
Financing Receivables Total | Industrial revenue bonds
Financing Receivables, By Class	14,559	14,003
Financing Receivables Total | Consumer auto
Financing Receivables, By Class	73,651	86,173
Financing Receivables Total | Home Equity Line of Credit
Financing Receivables, By Class	113,794	114,689
Financing Receivables Total | Land development
Financing Receivables, By Class	54,590	54,010
Financing Receivables Total | One- to four-family residential construction
Financing Receivables, By Class	48,161	42,793
Financing Receivables Total | Subdivision construction
Financing Receivables, By Class	7,297	30,894
Financing Receivables Total | Owner occupied one- to four-family residential
Financing Receivables, By Class	510,343	470,436
Financing Receivables Total | Non-owner occupied one- to four-family residential
Financing Receivables, By Class	130,609	114,569
Financing Receivables Total | Other residential
Financing Receivables, By Class	1,055,395	1,021,145
Financing Receivables Total | Commercial business
Financing Receivables, By Class	372,533	370,898
Financing Receivables Total | Consumer
Financing Receivables, By Class	39,724	40,762
Financing Receivables Total | Acquired Loans Net of Discount
Financing Receivables, By Class		98,643
Financing Receivables Total | Less Acquired Loans Net of Discount
Financing Receivables, By Class	91,934	98,643
Financing Receivables Total | Loans Receivable, Gross
Financing Receivables, By Class	5,216,114	5,225,529
Financing Receivables Total | Loans Receivable
Financing Receivables, By Class	$ 5,124,180	$ 5,126,886