Loans - Aging Categories of Loans by Segment (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Aging categories of loans by segment
Current	$ 1,333,509		$ 1,334,612
Past due 30 to 89 days	4,002		7,324
Past due 90 days or more & still accruing	791		2,047
Non-accrual	9,762		10,374
Total	1,348,064		1,354,357
Net deferred loan fees and discounts	1,076		1,187
Allowance for loan losses	(13,429)	$ (12,977)	(11,894)	$ (14,249)	$ (14,001)	$ (13,837)
Current loans, net	1,321,156		1,323,905
Loans, net	1,335,711		1,343,650
Commercial, financial, and agricultural
Aging categories of loans by segment
Current	171,344		153,737
Past due 30 to 89 days	245		249
Past due 90 days or more & still accruing	0		30
Non-accrual	1,565		2,197
Total	173,154		156,213
Allowance for loan losses	(1,979)	(1,953)	(1,779)	(1,786)	(1,584)	(1,680)
Real Estate Mortgages | Residential
Aging categories of loans by segment
Current	590,275		615,580
Past due 30 to 89 days	2,581		4,881
Past due 90 days or more & still accruing	595		1,529
Non-accrual	1,667		1,266
Total	595,118		623,256
Allowance for loan losses	(4,449)	(4,478)	(4,306)	(5,641)	(5,749)	(5,616)
Real Estate Mortgages | Commercial
Aging categories of loans by segment
Current	348,644		355,597
Past due 30 to 89 days	429		775
Past due 90 days or more & still accruing	196		164
Non-accrual	6,452		6,725
Total	355,721		363,261
Allowance for loan losses	(3,045)	(3,335)	(3,210)	(3,511)	(3,523)	(4,047)
Real Estate Mortgages | Construction
Aging categories of loans by segment
Current	43,142		37,871
Past due 30 to 89 days	0		131
Past due 90 days or more & still accruing	0		0
Non-accrual	58		65
Total	43,200		38,067
Allowance for loan losses	(170)	(150)	(118)	(156)	(132)	(143)
Consumer automobile loans
Aging categories of loans by segment
Current	159,810		149,703
Past due 30 to 89 days	374		709
Past due 90 days or more & still accruing	0		0
Non-accrual	17		105
Total	160,201		150,517
Allowance for loan losses	(1,997)	(2,214)	(1,780)	(1,374)	(1,435)	(1,328)
Other consumer installment loans
Aging categories of loans by segment
Current	20,294		22,124
Past due 30 to 89 days	373		579
Past due 90 days or more & still accruing	0		324
Non-accrual	3		16
Total	20,670		23,043
Allowance for loan losses	$ (255)	$ (127)	$ (278)	$ (242)	$ (240)	$ (259)