Fair Value Measurements - Other Real Estate Owned and Repossessed Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Total Gains (Losses)
Fair Value Measurements
Other real estate and repossessed assets	$ (12)	$ (106)
Gains (losses) on impaired loans	(55)
Total Gains (Losses) | Commercial real estate | Construction
Fair Value Measurements
Gains (losses) on impaired loans		0
Total Gains (Losses) | Commercial real estate | Mortgages
Fair Value Measurements
Gains (losses) on impaired loans	(22)
Total Gains (Losses) | Residential real estate | Mortgages
Fair Value Measurements
Gains (losses) on impaired loans	(19)
Total Gains (Losses) | Installment and other consumer
Fair Value Measurements
Gains (losses) on impaired loans	(14)
Nonrecurring | Total Fair Value
Fair Value Measurements
Impaired loans	5,590	3,127
Other real estate and repossessed assets	12,769	13,537
Nonrecurring | Total Fair Value | Commercial, financial, and agricultural
Fair Value Measurements
Impaired loans	2,422	1,263
Nonrecurring | Total Fair Value | Commercial real estate | Construction
Fair Value Measurements
Impaired loans	408	151
Nonrecurring | Total Fair Value | Commercial real estate | Mortgages
Fair Value Measurements
Impaired loans	827	233
Nonrecurring | Total Fair Value | Residential real estate | Mortgages
Fair Value Measurements
Impaired loans	1,921	1,480
Nonrecurring | Total Fair Value | Installment and other consumer
Fair Value Measurements
Impaired loans	12
Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Measurements
Impaired loans	0	0
Other real estate and repossessed assets	0	0
Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial, financial, and agricultural
Fair Value Measurements
Impaired loans	0	0
Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial real estate | Construction
Fair Value Measurements
Impaired loans	0	0
Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial real estate | Mortgages
Fair Value Measurements
Impaired loans	0	0
Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Residential real estate | Mortgages
Fair Value Measurements
Impaired loans	0	0
Nonrecurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Installment and other consumer
Fair Value Measurements
Impaired loans	0
Nonrecurring | Other Observable Inputs (Level 2)
Fair Value Measurements
Impaired loans	0	0
Other real estate and repossessed assets	0	0
Nonrecurring | Other Observable Inputs (Level 2) | Commercial, financial, and agricultural
Fair Value Measurements
Impaired loans	0	0
Nonrecurring | Other Observable Inputs (Level 2) | Commercial real estate | Construction
Fair Value Measurements
Impaired loans	0	0
Nonrecurring | Other Observable Inputs (Level 2) | Commercial real estate | Mortgages
Fair Value Measurements
Impaired loans	0	0
Nonrecurring | Other Observable Inputs (Level 2) | Residential real estate | Mortgages
Fair Value Measurements
Impaired loans	0	0
Nonrecurring | Other Observable Inputs (Level 2) | Installment and other consumer
Fair Value Measurements
Impaired loans	0
Nonrecurring | Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Impaired loans	5,590	3,127
Other real estate and repossessed assets	12,769	13,537
Nonrecurring | Significant Unobservable Inputs (Level 3) | Commercial, financial, and agricultural
Fair Value Measurements
Impaired loans	2,422	1,263
Nonrecurring | Significant Unobservable Inputs (Level 3) | Commercial real estate | Construction
Fair Value Measurements
Impaired loans	408	151
Nonrecurring | Significant Unobservable Inputs (Level 3) | Commercial real estate | Mortgages
Fair Value Measurements
Impaired loans	827	233
Nonrecurring | Significant Unobservable Inputs (Level 3) | Residential real estate | Mortgages
Fair Value Measurements
Impaired loans	1,921	$ 1,480
Nonrecurring | Significant Unobservable Inputs (Level 3) | Installment and other consumer
Fair Value Measurements
Impaired loans	$ 12