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