LOANS AND ALLOWANCE FOR LOAN LOSSES (Summary of Aging of the Loan Portfolio by Class) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Jan. 01, 2021	Dec. 31, 2020	Jan. 01, 2020
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 14,194,400		$ 13,929,049
Current, % of total loans	99.45%		99.34%
Greater Than 90 Days and Still Accruing	$ 9,776		$ 13,634
Greater than 90 Days and still Accruing, % of total loans	0.07%		0.10%
Nonaccrual	$ 41,866	$ 42,448	$ 42,448	$ 45,204
Nonaccrual, % of total loans	0.29%		0.30%
Total Loans	$ 14,272,280		$ 14,021,314
Total loans, % of total loans	100.00%		100.00%
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	$ 20,687		$ 27,024
Past Due, % of total loans	0.15%		0.19%
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	$ 5,551		$ 9,159
Past Due, % of total loans	0.04%		0.07%
Construction and Land Development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 880,139		$ 920,276
Greater Than 90 Days and Still Accruing	189		0
Nonaccrual	2,637	3,072	3,072	4,060
Total Loans	884,303		925,798
Construction and Land Development | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	865		1,903
Construction and Land Development | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	473		547
Commercial Real Estate - Owner Occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,069,019		2,114,804
Greater Than 90 Days and Still Accruing	3,180		3,727
Nonaccrual	7,016	7,128	7,128	13,889
Total Loans	2,083,155		2,128,909
Commercial Real Estate - Owner Occupied | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3,426		1,870
Commercial Real Estate - Owner Occupied | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	514		1,380
Commercial Real Estate - Non-Owner Occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	3,666,228		3,651,232
Greater Than 90 Days and Still Accruing	817		148
Nonaccrual	1,958	2,317	2,317	1,368
Total Loans	3,671,471		3,657,562
Commercial Real Estate - Non-Owner Occupied | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,055		2,144
Commercial Real Estate - Non-Owner Occupied | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,413		1,721
Multifamily Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	842,638		814,095
Greater Than 90 Days and Still Accruing	0		0
Nonaccrual	0	33	33	0
Total Loans	842,906		814,745
Multifamily Real Estate | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	187		617
Multifamily Real Estate | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	81		0
Commercial and Industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	3,593,508		3,257,201
Greater Than 90 Days and Still Accruing	654		1,114
Nonaccrual	2,023	2,107	2,107	3,037
Total Loans	3,599,884		3,263,460
Commercial and Industrial | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3,086		1,848
Commercial and Industrial | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	613		1,190
Residential 1-4 Family - Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	645,684		657,351
Greater Than 90 Days and Still Accruing	576		1,560
Nonaccrual	9,190	9,993	9,993	6,492
Total Loans	658,051		671,949
Residential 1-4 Family - Commercial | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,803		2,227
Residential 1-4 Family - Commercial | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	798		818
Residential 1-4 Family - Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	791,466		792,852
Greater Than 90 Days and Still Accruing	3,041		5,699
Nonaccrual	14,770	12,600	12,600	13,117
Total Loans	816,916		822,866
Residential 1-4 Family - Consumer | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	791,466		792,852
Residential 1-4 Family - Consumer | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	6,831		10,182
Total Loans	6,831		10,182
Residential 1-4 Family - Consumer | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	808		1,533
Total Loans	808		1,533
Residential 1-4 Family - Consumer | 90+ Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	3,041		5,699
Residential 1-4 Family - Consumer | Nonaccrual
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	14,770		12,600
Residential 1-4 Family - Revolving
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	557,335		587,522
Greater Than 90 Days and Still Accruing	917		826
Nonaccrual	3,853	4,629	4,629	2,490
Total Loans	563,786		596,996
Residential 1-4 Family - Revolving | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	557,335		587,522
Residential 1-4 Family - Revolving | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,397		2,975
Total Loans	1,397		2,975
Residential 1-4 Family - Revolving | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	284		1,044
Total Loans	284		1,044
Residential 1-4 Family - Revolving | 90+ Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	917		826
Residential 1-4 Family - Revolving | Nonaccrual
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	3,853		4,629
Auto
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	404,692		398,206
Greater Than 90 Days and Still Accruing	154		166
Nonaccrual	303	500	500	565
Total Loans	406,349		401,324
Auto | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	404,692		398,206
Auto | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1,035		2,076
Total Loans	1,035		2,076
Auto | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	165		376
Total Loans	165		376
Auto | 90+ Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	154		166
Auto | Nonaccrual
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	303		500
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	214,438		245,551
Greater Than 90 Days and Still Accruing	248		394
Nonaccrual	116	$ 69	69	88
Total Loans	215,711		247,730
Consumer | Current
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	214,438		245,551
Consumer | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	595		1,166
Total Loans	595		1,166
Consumer | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	314		550
Total Loans	314		550
Consumer | 90+ Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	248		394
Consumer | Nonaccrual
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	116		69
Other Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	529,253		489,959
Greater Than 90 Days and Still Accruing	0		0
Nonaccrual	0		0	$ 98
Total Loans	529,748		489,975
Other Commercial | 30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	407		16
Other Commercial | 60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	$ 88		$ 0