| LOANS AND ALLOWANCE FOR LOAN LOSSES (Summary of Aging of the Loan Portfolio by Class) (Details) - USD ($)$ in Thousands
 | Sep. 30, 2021 | Jan. 01, 2021 | Dec. 31, 2020 | Jan. 01, 2020 | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Greater Than 90 Days and Still Accruing | $ 11,030 |  | $ 13,634 |  | 
| Greater than 90 Days and still Accruing, % of total loans | 0.08% |  | 0.10% |  | 
| Nonaccrual | $ 35,472 | $ 42,448 | $ 42,448 | $ 45,204 | 
| Nonaccrual, % of total loans | 0.27% |  | 0.30% |  | 
| Total Loans | $ 13,139,586 |  | $ 14,021,314 |  | 
| Total loans, % of total loans | 100.00% |  | 100.00% |  | 
| Current |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | $ 13,065,331 |  | $ 13,929,049 |  | 
| Current, % of total loans | 99.43% |  | 99.34% |  | 
| 30 to 59 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | $ 19,144 |  | $ 27,024 |  | 
| Past Due, % of total loans | 0.15% |  | 0.19% |  | 
| 60 to 89 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | $ 8,609 |  | $ 9,159 |  | 
| Past Due, % of total loans | 0.07% |  | 0.07% |  | 
| Construction and Land Development |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Greater Than 90 Days and Still Accruing | $ 304 |  | $ 0 |  | 
| Nonaccrual | 2,710 | 3,072 | 3,072 | 4,060 | 
| Total Loans | 877,351 |  | 925,798 |  | 
| Construction and Land Development | Current |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 873,535 |  | 920,276 |  | 
| Construction and Land Development | 30 to 59 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 744 |  | 1,903 |  | 
| Construction and Land Development | 60 to 89 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 58 |  | 547 |  | 
| Commercial Real Estate - Owner Occupied |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Greater Than 90 Days and Still Accruing | 1,886 |  | 3,727 |  | 
| Nonaccrual | 7,786 | 7,128 | 7,128 | 13,889 | 
| Total Loans | 2,027,299 |  | 2,128,909 |  | 
| Commercial Real Estate - Owner Occupied | Current |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 2,016,831 |  | 2,114,804 |  | 
| Commercial Real Estate - Owner Occupied | 30 to 59 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 735 |  | 1,870 |  | 
| Commercial Real Estate - Owner Occupied | 60 to 89 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 61 |  | 1,380 |  | 
| Commercial Real Estate - Non-Owner Occupied |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Greater Than 90 Days and Still Accruing | 1,175 |  | 148 |  | 
| Nonaccrual | 4,174 | 2,317 | 2,317 | 1,368 | 
| Total Loans | 3,730,720 |  | 3,657,562 |  | 
| Commercial Real Estate - Non-Owner Occupied | Current |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 3,723,499 |  | 3,651,232 |  | 
| Commercial Real Estate - Non-Owner Occupied | 30 to 59 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 1,302 |  | 2,144 |  | 
| Commercial Real Estate - Non-Owner Occupied | 60 to 89 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 570 |  | 1,721 |  | 
| Multifamily Real Estate |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Greater Than 90 Days and Still Accruing | 0 |  | 0 |  | 
| Nonaccrual | 113 | 33 | 33 | 0 | 
| Total Loans | 776,287 |  | 814,745 |  | 
| Multifamily Real Estate | Current |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 776,174 |  | 814,095 |  | 
| Multifamily Real Estate | 30 to 59 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 0 |  | 617 |  | 
| Multifamily Real Estate | 60 to 89 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 0 |  | 0 |  | 
| Commercial and Industrial |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Greater Than 90 Days and Still Accruing | 1,256 |  | 1,114 |  | 
| Nonaccrual | 2,062 | 2,107 | 2,107 | 3,037 | 
| Total Loans | 2,580,190 |  | 3,263,460 |  | 
| Commercial and Industrial | Current |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 2,562,455 |  | 3,257,201 |  | 
| Commercial and Industrial | 30 to 59 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 11,089 |  | 1,848 |  | 
| Commercial and Industrial | 60 to 89 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 3,328 |  | 1,190 |  | 
| Residential 1-4 Family - Commercial |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Greater Than 90 Days and Still Accruing | 1,091 |  | 1,560 |  | 
| Nonaccrual | 2,445 | 9,993 | 9,993 | 6,492 | 
| Total Loans | 624,347 |  | 671,949 |  | 
| Residential 1-4 Family - Commercial | Current |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 619,306 |  | 657,351 |  | 
| Residential 1-4 Family - Commercial | 30 to 59 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 807 |  | 2,227 |  | 
| Residential 1-4 Family - Commercial | 60 to 89 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 698 |  | 818 |  | 
| Residential 1-4 Family - Mortgage |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Greater Than 90 Days and Still Accruing | 2,462 |  | 5,699 |  | 
| Nonaccrual | 12,150 | 12,600 | 12,600 | 13,117 | 
| Total Loans | 822,971 |  | 822,866 |  | 
| Residential 1-4 Family - Mortgage | Current |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 805,765 |  | 792,852 |  | 
| Total Loans | 805,765 |  | 792,852 |  | 
| Residential 1-4 Family - Mortgage | 30 to 59 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 406 |  | 10,182 |  | 
| Total Loans | 406 |  | 10,182 |  | 
| Residential 1-4 Family - Mortgage | 60 to 89 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 2,188 |  | 1,533 |  | 
| Total Loans | 2,188 |  | 1,533 |  | 
| Residential 1-4 Family - Mortgage | Greater Than 90 Days and still Accruing |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Total Loans | 2,462 |  | 5,699 |  | 
| Residential 1-4 Family - Mortgage | Nonaccrual |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Total Loans | 12,150 |  | 12,600 |  | 
| Residential 1-4 Family - Revolving |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Greater Than 90 Days and Still Accruing | 2,474 |  | 826 |  | 
| Nonaccrual | 3,723 | 4,629 | 4,629 | 2,490 | 
| Total Loans | 557,803 |  | 596,996 |  | 
| Residential 1-4 Family - Revolving | Current |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 549,927 |  | 587,522 |  | 
| Total Loans | 549,927 |  | 587,522 |  | 
| Residential 1-4 Family - Revolving | 30 to 59 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 1,092 |  | 2,975 |  | 
| Total Loans | 1,092 |  | 2,975 |  | 
| Residential 1-4 Family - Revolving | 60 to 89 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 587 |  | 1,044 |  | 
| Total Loans | 587 |  | 1,044 |  | 
| Residential 1-4 Family - Revolving | Greater Than 90 Days and still Accruing |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Total Loans | 2,474 |  | 826 |  | 
| Residential 1-4 Family - Revolving | Nonaccrual |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Total Loans | 3,723 |  | 4,629 |  | 
| Auto |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Greater Than 90 Days and Still Accruing | 209 |  | 166 |  | 
| Nonaccrual | 255 | 500 | 500 | 565 | 
| Total Loans | 425,436 |  | 401,324 |  | 
| Auto | Current |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 423,222 |  | 398,206 |  | 
| Total Loans | 423,222 |  | 398,206 |  | 
| Auto | 30 to 59 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 1,548 |  | 2,076 |  | 
| Total Loans | 1,548 |  | 2,076 |  | 
| Auto | 60 to 89 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 202 |  | 376 |  | 
| Total Loans | 202 |  | 376 |  | 
| Auto | Greater Than 90 Days and still Accruing |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Total Loans | 209 |  | 166 |  | 
| Auto | Nonaccrual |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Total Loans | 255 |  | 500 |  | 
| Consumer |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Greater Than 90 Days and Still Accruing | 173 |  | 394 |  | 
| Nonaccrual | 54 | $ 69 | 69 | 88 | 
| Total Loans | 182,039 |  | 247,730 |  | 
| Consumer | Current |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 180,705 |  | 245,551 |  | 
| Total Loans | 180,705 |  | 245,551 |  | 
| Consumer | 30 to 59 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 790 |  | 1,166 |  | 
| Total Loans | 790 |  | 1,166 |  | 
| Consumer | 60 to 89 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 317 |  | 550 |  | 
| Total Loans | 317 |  | 550 |  | 
| Consumer | Greater Than 90 Days and still Accruing |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Total Loans | 173 |  | 394 |  | 
| Consumer | Nonaccrual |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Total Loans | 54 |  | 69 |  | 
| Other Commercial |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Greater Than 90 Days and Still Accruing | 0 |  | 0 |  | 
| Nonaccrual | 0 |  | 0 | $ 98 | 
| Total Loans | 535,143 |  | 489,975 |  | 
| Other Commercial | Current |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 533,912 |  | 489,959 |  | 
| Other Commercial | 30 to 59 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | 631 |  | 16 |  | 
| Other Commercial | 60 to 89 Days Past Due |  |  |  |  | 
| Financing Receivable, Recorded Investment, Past Due [Line Items] |  |  |  |  | 
| Loans receivable, current and past due | $ 600 |  | $ 0 |  |