LOANS AND ALLOWANCE FOR CREDIT LOSSES - Financing Receivable Credit Quality Indicators (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Loan Portfolio Internal Grading System Classification	$ 5,225,529
Commercial construction
Loan Portfolio Internal Grading System Classification	1,212,837
Commercial Real Estate
Loan Portfolio Internal Grading System Classification	1,553,677
Industrial revenue bonds
Loan Portfolio Internal Grading System Classification	14,003
Consumer auto
Loan Portfolio Internal Grading System Classification	86,173
Consumer other
Loan Portfolio Internal Grading System Classification	40,762
Home Equity Line of Credit
Loan Portfolio Internal Grading System Classification	114,689
Land development
Loan Portfolio Internal Grading System Classification	54,010
One- to four-family residential construction
Loan Portfolio Internal Grading System Classification	42,793
Subdivision construction
Loan Portfolio Internal Grading System Classification	30,894
Owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	470,436
Non-owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	114,569
Other residential
Loan Portfolio Internal Grading System Classification	1,021,145
Commercial business
Loan Portfolio Internal Grading System Classification	370,898
Acquired Loans Net of Discount
Loan Portfolio Internal Grading System Classification	98,643
Satisfactory
Loan Portfolio Internal Grading System Classification	5,153,396
Satisfactory | Commercial construction
Loan Portfolio Internal Grading System Classification	1,212,837
Satisfactory | Commercial Real Estate
Loan Portfolio Internal Grading System Classification	1,498,031
Satisfactory | Industrial revenue bonds
Loan Portfolio Internal Grading System Classification	14,003
Satisfactory | Consumer auto
Loan Portfolio Internal Grading System Classification	85,657
Satisfactory | Consumer other
Loan Portfolio Internal Grading System Classification	40,514
Satisfactory | Home Equity Line of Credit
Loan Portfolio Internal Grading System Classification	114,049
Satisfactory | Land development
Loan Portfolio Internal Grading System Classification	54,010
Satisfactory | One- to four-family residential construction
Loan Portfolio Internal Grading System Classification	41,428
Satisfactory | Subdivision construction
Loan Portfolio Internal Grading System Classification	30,874
Satisfactory | Owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	467,855
Satisfactory | Non-owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	114,176
Satisfactory | Other residential
Loan Portfolio Internal Grading System Classification	1,017,648
Satisfactory | Commercial business
Loan Portfolio Internal Grading System Classification	363,681
Satisfactory | Acquired Loans Net of Discount
Loan Portfolio Internal Grading System Classification	98,633
Watch
Loan Portfolio Internal Grading System Classification	64,758
Watch | Commercial Real Estate
Loan Portfolio Internal Grading System Classification	52,208
Watch | Consumer auto
Loan Portfolio Internal Grading System Classification	5
Watch | Consumer other
Loan Portfolio Internal Grading System Classification	2
Watch | Home Equity Line of Credit
Loan Portfolio Internal Grading System Classification	39
Watch | One- to four-family residential construction
Loan Portfolio Internal Grading System Classification	1,365
Watch | Owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	216
Watch | Non-owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	324
Watch | Other residential
Loan Portfolio Internal Grading System Classification	3,497
Watch | Commercial business
Loan Portfolio Internal Grading System Classification	7,102
Special Mention
Loan Portfolio Internal Grading System Classification	0
Special Mention | Commercial construction
Loan Portfolio Internal Grading System Classification	0
Special Mention | Commercial Real Estate
Loan Portfolio Internal Grading System Classification	0
Special Mention | Industrial revenue bonds
Loan Portfolio Internal Grading System Classification	0
Special Mention | Consumer auto
Loan Portfolio Internal Grading System Classification	0
Special Mention | Consumer other
Loan Portfolio Internal Grading System Classification	0
Special Mention | Home Equity Line of Credit
Loan Portfolio Internal Grading System Classification	0
Special Mention | Land development
Loan Portfolio Internal Grading System Classification	0
Special Mention | One- to four-family residential construction
Loan Portfolio Internal Grading System Classification	0
Special Mention | Subdivision construction
Loan Portfolio Internal Grading System Classification	0
Special Mention | Owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	0
Special Mention | Non-owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	0
Special Mention | Other residential
Loan Portfolio Internal Grading System Classification	0
Special Mention | Commercial business
Loan Portfolio Internal Grading System Classification	0
Special Mention | Acquired Loans Net of Discount
Loan Portfolio Internal Grading System Classification	0
Substandard
Loan Portfolio Internal Grading System Classification	7,375
Substandard | Commercial Real Estate
Loan Portfolio Internal Grading System Classification	3,438
Substandard | Consumer auto
Loan Portfolio Internal Grading System Classification	511
Substandard | Consumer other
Loan Portfolio Internal Grading System Classification	246
Substandard | Home Equity Line of Credit
Loan Portfolio Internal Grading System Classification	601
Substandard | Subdivision construction
Loan Portfolio Internal Grading System Classification	20
Substandard | Owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	2,365
Substandard | Non-owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	69
Substandard | Commercial business
Loan Portfolio Internal Grading System Classification	115
Substandard | Acquired Loans Net of Discount
Loan Portfolio Internal Grading System Classification	10
Doubtful
Loan Portfolio Internal Grading System Classification	0
Doubtful | Commercial construction
Loan Portfolio Internal Grading System Classification	0
Doubtful | Commercial Real Estate
Loan Portfolio Internal Grading System Classification	0
Doubtful | Industrial revenue bonds
Loan Portfolio Internal Grading System Classification	0
Doubtful | Consumer auto
Loan Portfolio Internal Grading System Classification	0
Doubtful | Consumer other
Loan Portfolio Internal Grading System Classification	0
Doubtful | Home Equity Line of Credit
Loan Portfolio Internal Grading System Classification	0
Doubtful | Land development
Loan Portfolio Internal Grading System Classification	0
Doubtful | One- to four-family residential construction
Loan Portfolio Internal Grading System Classification	0
Doubtful | Subdivision construction
Loan Portfolio Internal Grading System Classification	0
Doubtful | Owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	0
Doubtful | Non-owner occupied one- to four-family residential
Loan Portfolio Internal Grading System Classification	0
Doubtful | Other residential
Loan Portfolio Internal Grading System Classification	0
Doubtful | Commercial business
Loan Portfolio Internal Grading System Classification	0
Doubtful | Acquired Loans Net of Discount
Loan Portfolio Internal Grading System Classification	$ 0