LOANS AND ALLOWANCE FOR LOAN LOSSES - Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Balance, Allowance				$ 25,791				$ 23,920	$ 25,791	$ 23,920	$ 21,062
Provision for loan losses	$ 3,661	$ 2,095	$ 9,110	1,801	$ 2,536	$ 1,787	$ 2,205	1,836	16,667	8,364	4,091
Loans charged off									(21,131)	(10,467)	(6,327)
Recoveries of loans previously charged off									7,492	3,974	5,094
Balance, Allowance	28,819				25,791				28,819	25,791	23,920
Ending balance, Loan	8,511,914				6,046,355				8,511,914	6,046,355	5,264,326
Loans individually evaluated for impairment												$ 4,964	$ 6,018	$ 6,407
Loans collectively evaluated for impairment												23,855	19,773	17,513
Balance, Allowance	28,819			25,791	25,791			23,920	25,791	23,920	21,062	28,819	25,791	23,920
Individually evaluated for impairment												53,892	52,231	60,421
Collectively evaluated for impairment												8,370,430	5,879,141	5,055,371
Acquired with deteriorated credit quality												87,592	114,983	148,534
Purchased Loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance, Allowance				3,253				1,626	3,253	1,626	0
Provision for loan losses									(2,164)	2,606	(232)
Loans charged off									(1,738)	(2,900)	(1,559)
Recoveries of loans previously charged off									2,582	1,921	3,417
Balance, Allowance	1,933				3,253				1,933	3,253	1,626
Ending balance, Loan	2,588,832				861,595				2,588,832	861,595	1,069,191
Loans individually evaluated for impairment												1,933	3,253	1,626
Loans collectively evaluated for impairment												0	0	0
Balance, Allowance	1,933			3,253	3,253			1,626	3,253	1,626	0	1,933	3,253	1,626
Individually evaluated for impairment												32,244	28,165	34,141
Collectively evaluated for impairment												2,468,996	718,447	886,516
Acquired with deteriorated credit quality												87,592	114,983	148,534
Nonaccrual loans												24,107	15,428
Troubled debt restructuring loans												2,499	3,635
Purchased Loan Pools
Allowance for Loan and Lease Losses [Roll Forward]
Balance, Allowance				1,075				1,837	1,075	1,837	581
Provision for loan losses									(343)	(762)	1,256
Loans charged off									0	0	0
Recoveries of loans previously charged off									0	0	0
Balance, Allowance	732				1,075				732	1,075	1,837
Ending balance, Loan	262,625				328,246				262,625	328,246	568,314
Loans individually evaluated for impairment												0	177	0
Loans collectively evaluated for impairment												732	898	1,837
Balance, Allowance	732			1,075	1,075			1,837	1,075	1,837	581	732	1,075	1,837
Individually evaluated for impairment												0	904	0
Collectively evaluated for impairment												262,625	327,342	568,314
Acquired with deteriorated credit quality												0	0	0
Commercial, financial and agricultural
Allowance for Loan and Lease Losses [Roll Forward]
Balance, Allowance				3,631				2,192	3,631	2,192	1,144
Provision for loan losses									10,690	3,019	2,647
Loans charged off									(13,803)	(2,850)	(1,999)
Recoveries of loans previously charged off									3,769	1,270	400
Balance, Allowance	4,287				3,631				4,287	3,631	2,192
Ending balance, Loan	1,316,359				1,362,508				1,316,359	1,362,508	967,138
Loans individually evaluated for impairment												570	465	120
Loans collectively evaluated for impairment												3,717	3,166	2,072
Balance, Allowance	4,287			3,631	3,631			2,192	3,631	2,192	1,144	4,287	3,631	2,192
Individually evaluated for impairment												3,211	2,971	501
Collectively evaluated for impairment												1,313,148	1,359,537	966,637
Acquired with deteriorated credit quality												0	0	0
Commercial, financial and agricultural | Purchased Loans
Allowance for Loan and Lease Losses [Roll Forward]
Nonaccrual loans												1,199	813
Troubled debt restructuring loans												63	5
Real estate – construction and development
Allowance for Loan and Lease Losses [Roll Forward]
Balance, Allowance				3,629				2,990	3,629	2,990	5,009
Provision for loan losses									277	488	(1,921)
Loans charged off									(292)	(95)	(588)
Recoveries of loans previously charged off									120	246	490
Balance, Allowance	3,734				3,629				3,734	3,629	2,990
Ending balance, Loan	671,198				624,595				671,198	624,595	363,045
Loans individually evaluated for impairment												3	48	266
Loans collectively evaluated for impairment												3,731	3,581	2,724
Balance, Allowance	3,734			3,629	3,629			2,990	3,629	2,990	5,009	3,734	3,629	2,990
Individually evaluated for impairment												424	500	659
Collectively evaluated for impairment												670,774	624,095	362,386
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												6,119	3,139
Troubled debt restructuring loans												0	0
Real estate – commercial and farmland
Allowance for Loan and Lease Losses [Roll Forward]
Balance, Allowance				7,501				7,662	7,501	7,662	7,994
Provision for loan losses									1,636	508	107
Loans charged off									(338)	(853)	(708)
Recoveries of loans previously charged off									176	184	269
Balance, Allowance	8,975				7,501				8,975	7,501	7,662
Ending balance, Loan	1,814,529				1,535,439				1,814,529	1,535,439	1,406,219
Loans individually evaluated for impairment												1,591	1,047	1,502
Loans collectively evaluated for impairment												7,384	6,454	6,160
Balance, Allowance	8,975			7,501	7,501			7,662	7,501	7,662	7,994	8,975	7,501	7,662
Individually evaluated for impairment												6,649	8,873	12,423
Collectively evaluated for impairment												1,807,880	1,526,566	1,393,796
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												5,534	5,685
Troubled debt restructuring loans												71	1,311
Real estate – residential
Allowance for Loan and Lease Losses [Roll Forward]
Balance, Allowance				4,786				6,786	4,786	6,786	4,760
Provision for loan losses									1,002	(86)	2,757
Loans charged off									(771)	(2,151)	(1,122)
Recoveries of loans previously charged off									346	237	391
Balance, Allowance	5,363				4,786				5,363	4,786	6,786
Ending balance, Loan	1,403,000				1,009,461				1,403,000	1,009,461	781,018
Loans individually evaluated for impairment												867	1,028	2,893
Loans collectively evaluated for impairment												4,496	3,758	3,893
Balance, Allowance	5,363			4,786	4,786			6,786	4,786	6,786	4,760	5,363	4,786	6,786
Individually evaluated for impairment												11,364	10,818	12,697
Collectively evaluated for impairment												1,391,636	998,643	768,321
Acquired with deteriorated credit quality												0	0	0
Real estate – residential | Purchased Loans
Allowance for Loan and Lease Losses [Roll Forward]
Nonaccrual loans												10,769	5,743
Troubled debt restructuring loans												2,351	2,319
Consumer Installment
Allowance for Loan and Lease Losses [Roll Forward]
Balance, Allowance				1,916				827	1,916	827	1,574
Provision for loan losses									5,569	2,591	(523)
Loans charged off									(4,189)	(1,618)	(351)
Recoveries of loans previously charged off									499	116	127
Balance, Allowance	3,795				1,916				3,795	1,916	827
Ending balance, Loan	455,371				324,511				455,371	324,511	109,401
Loans individually evaluated for impairment												0	0	0
Loans collectively evaluated for impairment												3,795	1,916	827
Balance, Allowance	$ 3,795			$ 1,916	$ 1,916			$ 827	$ 1,916	$ 827	$ 1,574	3,795	1,916	827
Individually evaluated for impairment												0	0	0
Collectively evaluated for impairment												455,371	324,511	109,401
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