Fair Value Measurements - Other Real Estate Owned and Repossessed Assets (Details) - Nonrecurring - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Total Fair Value
Fair Value Measurements
Impaired loans	$ 2,480	$ 3,262	$ 2,480	$ 3,262
Other real estate and repossessed assets	12,878	13,373	12,878	13,373
Total Fair Value | Commercial, financial, and agricultural
Fair Value Measurements
Impaired loans	529	1,549	529	1,549
Total Fair Value | Commercial real estate | Construction
Fair Value Measurements
Impaired loans	145	158	145	158
Total Fair Value | Commercial real estate | Mortgages
Fair Value Measurements
Impaired loans	860	399	860	399
Total Fair Value | Residential real estate | Mortgages
Fair Value Measurements
Impaired loans	933	1,156	933	1,156
Total Fair Value | Installment and other consumer
Fair Value Measurements
Impaired loans	13	0	13	0
Total Gains (Losses)
Fair Value Measurements
Gains (losses) on impaired loans	(77)	(53)	(204)	(303)
Gains (losses) on other real estate owned and repossessed assets	10	(3)	(166)	(29)
Total Gains (Losses) | Commercial, financial, and agricultural
Fair Value Measurements
Gains (losses) on impaired loans	(22)	(21)	(132)	(187)
Total Gains (Losses) | Commercial real estate | Construction
Fair Value Measurements
Gains (losses) on impaired loans	0	0	0	(27)
Total Gains (Losses) | Commercial real estate | Mortgages
Fair Value Measurements
Gains (losses) on impaired loans	(6)	0	(15)	(20)
Total Gains (Losses) | Residential real estate | Mortgages
Fair Value Measurements
Gains (losses) on impaired loans	(45)	(32)	(45)	(44)
Total Gains (Losses) | Installment and other consumer
Fair Value Measurements
Gains (losses) on impaired loans	(4)	0	(12)	(25)
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
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial, financial, and agricultural
Fair Value Measurements
Impaired loans	0	0	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial real estate | Construction
Fair Value Measurements
Impaired loans	0	0	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial real estate | Mortgages
Fair Value Measurements
Impaired loans	0	0	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Residential real estate | Mortgages
Fair Value Measurements
Impaired loans	0	0	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Installment and other consumer
Fair Value Measurements
Impaired loans	0	0	0	0
Other Observable Inputs (Level 2)
Fair Value Measurements
Impaired loans	0	0	0	0
Other real estate and repossessed assets	0	0	0	0
Other Observable Inputs (Level 2) | Commercial, financial, and agricultural
Fair Value Measurements
Impaired loans	0	0	0	0
Other Observable Inputs (Level 2) | Commercial real estate | Construction
Fair Value Measurements
Impaired loans	0	0	0	0
Other Observable Inputs (Level 2) | Commercial real estate | Mortgages
Fair Value Measurements
Impaired loans	0	0	0	0
Other Observable Inputs (Level 2) | Residential real estate | Mortgages
Fair Value Measurements
Impaired loans	0	0	0	0
Other Observable Inputs (Level 2) | Installment and other consumer
Fair Value Measurements
Impaired loans	0	0	0	0
Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Impaired loans	2,480	3,262	2,480	3,262
Other real estate and repossessed assets	12,878	13,373	12,878	13,373
Significant Unobservable Inputs (Level 3) | Commercial, financial, and agricultural
Fair Value Measurements
Impaired loans	529	1,549	529	1,549
Significant Unobservable Inputs (Level 3) | Commercial real estate | Construction
Fair Value Measurements
Impaired loans	145	158	145	158
Significant Unobservable Inputs (Level 3) | Commercial real estate | Mortgages
Fair Value Measurements
Impaired loans	860	399	860	399
Significant Unobservable Inputs (Level 3) | Residential real estate | Mortgages
Fair Value Measurements
Impaired loans	933	1,156	933	1,156
Significant Unobservable Inputs (Level 3) | Installment and other consumer
Fair Value Measurements
Impaired loans	$ 13	$ 0	$ 13	$ 0