ALLOWANCE FOR LOAN AND LEASE LOSSES (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in the allowance
Beginning balance				$ 56,631				$ 63,314	$ 56,631	$ 63,314	$ 74,040
Provision (credit) for loan and lease losses	$ (186)	$ (126)	$ (2,282)	(80)	$ (2,645)	$ (743)	$ (1,382)	(747)	(2,674)	(5,517)	(15,671)
Subtotal									53,957	57,797	58,369
Charge-offs									8,071	6,862	11,256
Recoveries									4,115	5,696	16,201
Net charge-offs (recoveries)									3,956	1,166	(4,945)
Ending balance	50,001				56,631				50,001	56,631	63,314
Commercial, financial & agricultural
Changes in the allowance
Beginning balance				8,637				6,905	8,637	6,905	8,954
Provision (credit) for loan and lease losses									(705)	1,217	(1,179)
Subtotal									7,932	8,122	7,775
Charge-offs									1,704	1,599	5,658
Recoveries									1,366	2,114	4,788
Net charge-offs (recoveries)									338	(515)	870
Ending balance	7,594				8,637				7,594	8,637	6,905
Real estate | Construction
Changes in the allowance
Beginning balance				4,224				8,454	4,224	8,454	14,969
Provision (credit) for loan and lease losses									(2,558)	(4,363)	(7,395)
Subtotal									1,666	4,091	7,574
Charge-offs									0	0	0
Recoveries									169	133	880
Net charge-offs (recoveries)									(169)	(133)	(880)
Ending balance	1,835				4,224				1,835	4,224	8,454
Real estate | Residential mortgage
Changes in the allowance
Beginning balance				15,055				14,642	15,055	14,642	15,031
Provision (credit) for loan and lease losses									(1,533)	(282)	(1,510)
Subtotal									13,522	14,360	13,521
Charge-offs									73	0	0
Recoveries									879	695	1,121
Net charge-offs (recoveries)									(806)	(695)	(1,121)
Ending balance	14,328				15,055				14,328	15,055	14,642
Real estate | Home equity
Changes in the allowance
Beginning balance				3,502				3,096	3,502	3,096	2,896
Provision (credit) for loan and lease losses									(229)	391	(746)
Subtotal									3,273	3,487	2,150
Charge-offs									0	0	110
Recoveries									44	15	1,056
Net charge-offs (recoveries)									(44)	(15)	(946)
Ending balance	3,317				3,502				3,317	3,502	3,096
Real estate | Commercial mortgage
Changes in the allowance
Beginning balance				19,104				21,847	19,104	21,847	20,869
Provision (credit) for loan and lease losses									(2,460)	(3,558)	(4,903)
Subtotal									16,644	18,289	15,966
Charge-offs									0	209	838
Recoveries									157	1,024	6,719
Net charge-offs (recoveries)									(157)	(815)	(5,881)
Ending balance	16,801				19,104				16,801	19,104	21,847
Consumer | Other
Changes in the allowance
Beginning balance				6,109				6,230	6,109	6,230	7,314
Provision (credit) for loan and lease losses									4,811	3,218	1,956
Subtotal									10,920	9,448	9,270
Charge-offs									6,294	5,054	4,650
Recoveries									1,500	1,715	1,610
Net charge-offs (recoveries)									4,794	3,339	3,040
Ending balance	6,126				6,109				6,126	6,109	6,230
Leases
Changes in the allowance
Beginning balance				0				0	0	0	7
Provision (credit) for loan and lease losses									0	0	(34)
Subtotal									0	0	(27)
Charge-offs										0	0
Recoveries									0	0	27
Net charge-offs (recoveries)									0	0	(27)
Ending balance	0				0				0	0	0
Unallocated
Changes in the allowance
Beginning balance				$ 0				$ 2,140	0	2,140	4,000
Provision (credit) for loan and lease losses									0	(2,140)	(1,860)
Subtotal									0	0	2,140
Charge-offs									0	0	0
Recoveries									0	0	0
Net charge-offs (recoveries)									0	0	0
Ending balance	$ 0				$ 0				$ 0	$ 0	$ 2,140