Loans - Aging Categories of Loans by Segment (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Aging categories of loans by segment
Current	$ 1,334,905		$ 1,334,612
Past due 30 to 89 days	2,405		7,324
Past due 90 days or more & still accruing	1,279		2,047
Non-accrual	9,818		10,374
Total	1,348,407		1,354,357
Net deferred loan fees and discounts	940		1,187
Allowance for loan losses	(12,977)	$ (12,500)	(11,894)	$ (14,001)	$ (13,792)	$ (13,837)
Current loans, net	1,322,868		1,323,905
Loans, net	1,336,370		1,343,650
Commercial, financial, and agricultural
Aging categories of loans by segment
Current	167,025		153,737
Past due 30 to 89 days	41		249
Past due 90 days or more & still accruing	2		30
Non-accrual	1,836		2,197
Total	168,904		156,213
Allowance for loan losses	(1,953)	(1,897)	(1,779)	(1,584)	(1,732)	(1,680)
Real Estate Mortgages | Residential
Aging categories of loans by segment
Current	602,480		615,580
Past due 30 to 89 days	1,709		4,881
Past due 90 days or more & still accruing	933		1,529
Non-accrual	1,092		1,266
Total	606,214		623,256
Allowance for loan losses	(4,478)	(4,537)	(4,306)	(5,749)	(5,730)	(5,616)
Real Estate Mortgages | Commercial
Aging categories of loans by segment
Current	345,638		355,597
Past due 30 to 89 days	25		775
Past due 90 days or more & still accruing	331		164
Non-accrual	6,536		6,725
Total	352,530		363,261
Allowance for loan losses	(3,335)	(3,414)	(3,210)	(3,523)	(3,802)	(4,047)
Real Estate Mortgages | Construction
Aging categories of loans by segment
Current	43,960		37,871
Past due 30 to 89 days	0		131
Past due 90 days or more & still accruing	0		0
Non-accrual	60		65
Total	44,020		38,067
Allowance for loan losses	(150)	(160)	(118)	(132)	(130)	(143)
Consumer automobile loans
Aging categories of loans by segment
Current	155,219		149,703
Past due 30 to 89 days	199		709
Past due 90 days or more & still accruing	9		0
Non-accrual	294		105
Total	155,721		150,517
Allowance for loan losses	(2,214)	(1,855)	(1,780)	(1,435)	(1,402)	(1,328)
Other consumer installment loans
Aging categories of loans by segment
Current	20,583		22,124
Past due 30 to 89 days	431		579
Past due 90 days or more & still accruing	4		324
Non-accrual	0		16
Total	21,018		23,043
Allowance for loan losses	$ (127)	$ (267)	$ (278)	$ (240)	$ (278)	$ (259)