LOANS AND ALLOWANCE FOR LOAN LOSSES - Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allowance for Loan and Lease Losses [Roll Forward]
Balance, Allowance				$ 28,819				$ 25,791	$ 28,819	$ 25,791	$ 23,920
Provision for loan losses	$ 5,693	$ 5,989	$ 4,668	3,408	$ 3,661	$ 2,095	$ 9,110	1,801	19,758	16,667	8,364
Loans charged off									(19,788)	(21,131)	(10,467)
Recoveries of loans previously charged off									9,400	7,492	3,974
Balance, Allowance	38,189				28,819				38,189	28,819	25,791
Ending balance, Loan	12,818,476				8,511,914				12,818,476	8,511,914	6,046,355
Loans individually evaluated for impairment												$ 7,162	$ 4,964	$ 6,018
Loans collectively evaluated for impairment												31,027	23,855	19,773
Balance, Allowance	38,189			28,819	28,819			25,791	28,819	28,819	23,920	38,189	28,819	25,791
Individually evaluated for impairment												82,475	53,892	52,231
Collectively evaluated for impairment												12,602,078	8,370,430	5,879,141
Acquired with deteriorated credit quality												133,923	87,592	114,983
Purchased Loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance, Allowance				1,933				3,253	1,933	3,253	1,626
Provision for loan losses									1,418	(2,164)	2,606
Loans charged off									(5,051)	(1,738)	(2,900)
Recoveries of loans previously charged off									4,985	2,582	1,921
Balance, Allowance	3,285				1,933				3,285	1,933	3,253
Ending balance, Loan	5,075,281				2,588,832				5,075,281	2,588,832	861,595
Loans individually evaluated for impairment												3,285	1,933	3,253
Loans collectively evaluated for impairment												0	0	0
Balance, Allowance	3,285			1,933	1,933			3,253	1,933	1,933	1,626	3,285	1,933	3,253
Individually evaluated for impairment												42,242	32,244	28,165
Collectively evaluated for impairment												4,899,116	2,468,996	718,447
Acquired with deteriorated credit quality												133,923	87,592	114,983
Nonaccrual loans												45,023	24,107
Troubled debt restructuring loans												3,725	2,499
Purchased Loan Pools
Allowance for Loan and Lease Losses [Roll Forward]
Balance, Allowance				732				1,075	732	1,075	1,837
Provision for loan losses									(108)	(343)	(762)
Loans charged off									0	0	0
Recoveries of loans previously charged off									0	0	0
Balance, Allowance	624				732				624	732	1,075
Ending balance, Loan	213,208				262,625				213,208	262,625	328,246
Loans individually evaluated for impairment												0	0	177
Loans collectively evaluated for impairment												624	732	898
Balance, Allowance	624			732	732			1,075	732	732	1,837	624	732	1,075
Individually evaluated for impairment												810	0	904
Collectively evaluated for impairment												212,398	262,625	327,342
Acquired with deteriorated credit quality												0	0	0
Commercial, financial and agricultural
Allowance for Loan and Lease Losses [Roll Forward]
Balance, Allowance				4,287				3,631	4,287	3,631	2,192
Provision for loan losses									6,699	10,690	3,019
Loans charged off									(7,131)	(13,803)	(2,850)
Recoveries of loans previously charged off									3,072	3,769	1,270
Balance, Allowance	6,927				4,287				6,927	4,287	3,631
Ending balance, Loan	1,646,438				1,316,359				1,646,438	1,316,359	1,362,508
Loans individually evaluated for impairment												1,627	570	465
Loans collectively evaluated for impairment												5,300	3,717	3,166
Balance, Allowance	6,927			4,287	4,287			3,631	4,287	4,287	2,192	6,927	4,287	3,631
Individually evaluated for impairment												9,483	3,211	2,971
Collectively evaluated for impairment												1,636,955	1,313,148	1,359,537
Acquired with deteriorated credit quality												0	0	0
Commercial, financial and agricultural | Purchased Loans
Allowance for Loan and Lease Losses [Roll Forward]
Nonaccrual loans												5,933	1,199
Troubled debt restructuring loans												0	63
Real estate – construction and development
Allowance for Loan and Lease Losses [Roll Forward]
Balance, Allowance				3,734				3,629	3,734	3,629	2,990
Provision for loan losses									2,421	277	488
Loans charged off									(321)	(292)	(95)
Recoveries of loans previously charged off									25	120	246
Balance, Allowance	5,859				3,734				5,859	3,734	3,629
Ending balance, Loan	1,083,564				671,198				1,083,564	671,198	624,595
Loans individually evaluated for impairment												68	3	48
Loans collectively evaluated for impairment												5,791	3,731	3,581
Balance, Allowance	5,859			3,734	3,734			3,629	3,734	3,734	2,990	5,859	3,734	3,629
Individually evaluated for impairment												598	424	500
Collectively evaluated for impairment												1,082,966	670,774	624,095
Acquired with deteriorated credit quality												0	0	0
Real estate – construction and development | Purchased Loans
Allowance for Loan and Lease Losses [Roll Forward]
Nonaccrual loans												842	6,119
Troubled debt restructuring loans												0	0
Real estate – commercial and farmland
Allowance for Loan and Lease Losses [Roll Forward]
Balance, Allowance				8,975				7,501	8,975	7,501	7,662
Provision for loan losses									1,446	1,636	508
Loans charged off									(1,430)	(338)	(853)
Recoveries of loans previously charged off									113	176	184
Balance, Allowance	9,104				8,975				9,104	8,975	7,501
Ending balance, Loan	2,447,834				1,814,529				2,447,834	1,814,529	1,535,439
Loans individually evaluated for impairment												392	1,591	1,047
Loans collectively evaluated for impairment												8,712	7,384	6,454
Balance, Allowance	9,104			8,975	8,975			7,501	8,975	7,501	7,501	9,104	8,975	7,501
Individually evaluated for impairment												6,344	6,649	8,873
Collectively evaluated for impairment												2,441,490	1,807,880	1,526,566
Acquired with deteriorated credit quality												0	0	0
Real estate – commercial and farmland | Purchased Loans
Allowance for Loan and Lease Losses [Roll Forward]
Nonaccrual loans												19,565	5,534
Troubled debt restructuring loans												0	71
Real estate – residential
Allowance for Loan and Lease Losses [Roll Forward]
Balance, Allowance				5,363				4,786	5,363	4,786	6,786
Provision for loan losses									3,108	1,002	(86)
Loans charged off									(160)	(771)	(2,151)
Recoveries of loans previously charged off									295	346	237
Balance, Allowance	8,606				5,363				8,606	5,363	4,786
Ending balance, Loan	1,901,352				1,403,000				1,901,352	1,403,000	1,009,461
Loans individually evaluated for impairment												1,790	867	1,028
Loans collectively evaluated for impairment												6,816	4,496	3,758
Balance, Allowance	8,606			5,363	5,363			4,786	5,363	4,786	4,786	8,606	5,363	4,786
Individually evaluated for impairment												22,998	11,364	10,818
Collectively evaluated for impairment												1,878,354	1,391,636	998,643
Acquired with deteriorated credit quality												0	0	0
Real estate – residential | Purchased Loans
Allowance for Loan and Lease Losses [Roll Forward]
Nonaccrual loans												16,560	10,769
Troubled debt restructuring loans												3,691	2,351
Consumer Installment
Allowance for Loan and Lease Losses [Roll Forward]
Balance, Allowance				3,795				1,916	3,795	1,916	827
Provision for loan losses									4,774	5,569	2,591
Loans charged off									(5,695)	(4,189)	(1,618)
Recoveries of loans previously charged off									910	499	116
Balance, Allowance	3,784				3,795				3,784	3,795	1,916
Ending balance, Loan	450,799				455,371				450,799	455,371	324,511
Loans individually evaluated for impairment												0	0	0
Loans collectively evaluated for impairment												3,784	3,795	1,916
Balance, Allowance	$ 3,784			$ 3,795	$ 3,795			$ 1,916	$ 3,795	$ 1,916	$ 1,916	3,784	3,795	1,916
Individually evaluated for impairment												0	0	0
Collectively evaluated for impairment												450,799	455,371	324,511
Acquired with deteriorated credit quality												0	0	0
Substandard | Minimum
Allowance for Loan and Lease Losses [Roll Forward]
Nonaccrual loans												100	100	100
Troubled debt restructuring loans												$ 100	$ 100	$ 100