LOAN CREDIT QUALITY AND RELATED ALLOWANCE FOR LOAN LOSSES - Credit Quality Categories (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Credit quality categories
Total	$ 1,246,342	$ 1,094,938
Commercial, Financial, and Agricultural
Credit quality categories
Total	178,885	146,110
Residential Real Estate Mortgage
Credit quality categories
Total	597,077	564,740
Commercial Real Estate Mortgage
Credit quality categories
Total	332,019	306,182
Construction Real Estate Mortgage
Credit quality categories
Total	31,683	34,650
Installment Loans to Individuals
Credit quality categories
Total	106,678	43,256
Pass
Credit quality categories
Total	1,218,853	1,057,602
Pass | Commercial, Financial, and Agricultural
Credit quality categories
Total	175,603	140,497
Pass | Residential Real Estate Mortgage
Credit quality categories
Total	593,828	561,440
Pass | Commercial Real Estate Mortgage
Credit quality categories
Total	311,209	277,916
Pass | Construction Real Estate Mortgage
Credit quality categories
Total	31,535	34,493
Pass | Installment Loans to Individuals
Credit quality categories
Total	106,678	43,256
Special Mention
Credit quality categories
Total	9,118	14,826
Special Mention | Commercial, Financial, and Agricultural
Credit quality categories
Total	738	2,943
Special Mention | Residential Real Estate Mortgage
Credit quality categories
Total	1,043	740
Special Mention | Commercial Real Estate Mortgage
Credit quality categories
Total	7,337	11,143
Special Mention | Construction Real Estate Mortgage
Credit quality categories
Total	0	0
Special Mention | Installment Loans to Individuals
Credit quality categories
Total	0	0
Substandard
Credit quality categories
Total	18,371	22,510
Substandard | Commercial, Financial, and Agricultural
Credit quality categories
Total	2,544	2,670
Substandard | Residential Real Estate Mortgage
Credit quality categories
Total	2,206	2,560
Substandard | Commercial Real Estate Mortgage
Credit quality categories
Total	13,473	17,123
Substandard | Construction Real Estate Mortgage
Credit quality categories
Total	148	157
Substandard | Installment Loans to Individuals
Credit quality categories
Total	$ 0	$ 0