LOANS - Analysis of Past-Due Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	$ 169,434	$ 184,006
Current Loans	14,774,159	12,634,470
Total Loans	14,943,593	12,818,476	$ 12,826,284
Loans 90 Days or More Past Due and Still Accruing	7,003	5,754
Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	51,015	88,291
Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	18,823	32,582
Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	99,596	63,133
Commercial, financial and agricultural
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	13,142	12,344
Current Loans	1,866,646	789,827
Total Loans	1,879,788	802,171	931,755
Loans 90 Days or More Past Due and Still Accruing	0	0
Commercial, financial and agricultural | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	6,419	3,609
Commercial, financial and agricultural | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	1,892	2,251
Commercial, financial and agricultural | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	4,831	6,484
Consumer installment
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	5,935	6,276
Current Loans	444,875	492,301
Total Loans	450,810	498,577	500,067
Loans 90 Days or More Past Due and Still Accruing	1,305	922
Consumer installment | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	2,552	3,488
Consumer installment | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	1,441	1,336
Consumer installment | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	1,942	1,452
Indirect automobile
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	4,839	8,567
Current Loans	677,557	1,053,257
Total Loans	682,396	1,061,824	1,111,815
Loans 90 Days or More Past Due and Still Accruing	0	21
Indirect automobile | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	2,603	5,978
Indirect automobile | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	796	1,067
Indirect automobile | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	1,440	1,522
Mortgage warehouse
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	0	0
Current Loans	995,942	526,369
Total Loans	995,942	526,369	562,598
Loans 90 Days or More Past Due and Still Accruing	0	0
Mortgage warehouse | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	0	0
Mortgage warehouse | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	0	0
Mortgage warehouse | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	0	0
Municipal
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	0	0
Current Loans	725,669	564,304
Total Loans	725,669	564,304	578,267
Loans 90 Days or More Past Due and Still Accruing	0	0
Municipal | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	0	0
Municipal | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	0	0
Municipal | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	0	0
Premium finance
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	13,694	27,234
Current Loans	697,196	627,435
Total Loans	710,890	654,669	656,570
Loans 90 Days or More Past Due and Still Accruing	3,774	4,811
Premium finance | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	5,403	13,801
Premium finance | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	4,517	8,022
Premium finance | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	3,774	5,411
Real estate – construction and development
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	16,420	10,592
Current Loans	1,611,835	1,538,470
Total Loans	1,628,255	1,549,062	1,468,696
Loans 90 Days or More Past Due and Still Accruing	1,883	0
Real estate – construction and development | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	7,268	7,785
Real estate – construction and development | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	4,700	1,224
Real estate – construction and development | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	4,452	1,583
Real estate – commercial and farmland
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	21,338	26,407
Current Loans	5,094,914	4,326,632
Total Loans	5,116,252	4,353,039	4,198,759
Loans 90 Days or More Past Due and Still Accruing	0	0
Real estate – commercial and farmland | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	9,962	7,404
Real estate – commercial and farmland | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	1,407	3,405
Real estate – commercial and farmland | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	9,969	15,598
Real estate – residential
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	94,066	92,586
Current Loans	2,659,525	2,715,875
Total Loans	2,753,591	2,808,461	$ 2,817,757
Loans 90 Days or More Past Due and Still Accruing	41	0
Real estate – residential | Loans 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	16,808	46,226
Real estate – residential | Loans 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	4,070	15,277
Real estate – residential | Loans 90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans Past Due	$ 73,188	$ 31,083