Fair Value Measurements - Other Real Estate Owned and Repossessed Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Total Gains (Losses)
Fair Value Measurements
Gains (losses) on impaired loans	$ (37)	$ (119)	$ (92)	$ (126)
Gains (losses) on other real estate owned and repossessed assets	213	(70)	199	(176)
Total Gains (Losses) | Commercial, financial, and agricultural
Fair Value Measurements
Gains (losses) on impaired loans		(110)		(110)
Total Gains (Losses) | Commercial real estate | Construction
Fair Value Measurements
Gains (losses) on impaired loans		0		0
Total Gains (Losses) | Commercial real estate | Mortgages
Fair Value Measurements
Gains (losses) on impaired loans	(2)	(6)	(24)	(9)
Total Gains (Losses) | Residential real estate | Mortgages
Fair Value Measurements
Gains (losses) on impaired loans	(32)		(51)
Total Gains (Losses) | Installment and other consumer
Fair Value Measurements
Gains (losses) on impaired loans	(3)	(3)	(17)	(7)
Nonrecurring | Total Fair Value
Fair Value Measurements
Impaired loans	6,591	3,500	6,591	3,500
Other real estate and repossessed assets	12,520	13,110	12,520	13,110
Nonrecurring | Total Fair Value | Commercial, financial, and agricultural
Fair Value Measurements
Impaired loans	2,408	1,244	2,408	1,244
Nonrecurring | Total Fair Value | Commercial real estate | Construction
Fair Value Measurements
Impaired loans	837	146	837	146
Nonrecurring | Total Fair Value | Commercial real estate | Mortgages
Fair Value Measurements
Impaired loans	1,304	863	1,304	863
Nonrecurring | Total Fair Value | Residential real estate | Mortgages
Fair Value Measurements
Impaired loans	2,031	1,247	2,031	1,247
Nonrecurring | Total Fair Value | Installment and other consumer
Fair Value Measurements
Impaired loans	11	0	11	0
Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Measurements
Impaired loans	0	0	0	0
Other real estate and repossessed assets	0	0	0	0
Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial, financial, and agricultural
Fair Value Measurements
Impaired loans	0	0	0	0
Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial real estate | Construction
Fair Value Measurements
Impaired loans	0	0	0	0
Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial real estate | Mortgages
Fair Value Measurements
Impaired loans	0	0	0	0
Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Residential real estate | Mortgages
Fair Value Measurements
Impaired loans	0	0	0	0
Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Installment and other consumer
Fair Value Measurements
Impaired loans	0	0	0	0
Nonrecurring | Other Observable Inputs (Level 2)
Fair Value Measurements
Impaired loans	0	0	0	0
Other real estate and repossessed assets	0	0	0	0
Nonrecurring | Other Observable Inputs (Level 2) | Commercial, financial, and agricultural
Fair Value Measurements
Impaired loans	0	0	0	0
Nonrecurring | Other Observable Inputs (Level 2) | Commercial real estate | Construction
Fair Value Measurements
Impaired loans	0	0	0	0
Nonrecurring | Other Observable Inputs (Level 2) | Commercial real estate | Mortgages
Fair Value Measurements
Impaired loans	0	0	0	0
Nonrecurring | Other Observable Inputs (Level 2) | Residential real estate | Mortgages
Fair Value Measurements
Impaired loans	0	0	0	0
Nonrecurring | Other Observable Inputs (Level 2) | Installment and other consumer
Fair Value Measurements
Impaired loans	0	0	0	0
Nonrecurring | Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Impaired loans	6,591	3,500	6,591	3,500
Other real estate and repossessed assets	12,520	13,110	12,520	13,110
Nonrecurring | Significant Unobservable Inputs (Level 3) | Commercial, financial, and agricultural
Fair Value Measurements
Impaired loans	2,408	1,244	2,408	1,244
Nonrecurring | Significant Unobservable Inputs (Level 3) | Commercial real estate | Construction
Fair Value Measurements
Impaired loans	837	146	837	146
Nonrecurring | Significant Unobservable Inputs (Level 3) | Commercial real estate | Mortgages
Fair Value Measurements
Impaired loans	1,304	863	1,304	863
Nonrecurring | Significant Unobservable Inputs (Level 3) | Residential real estate | Mortgages
Fair Value Measurements
Impaired loans	2,031	1,247	2,031	1,247
Nonrecurring | Significant Unobservable Inputs (Level 3) | Installment and other consumer
Fair Value Measurements
Impaired loans	$ 11	$ 0	$ 11	$ 0