Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Capital Stock [Member]	Surplus [Member]	Undivided Profits [Member]	Accumulated Other Comprehensive Loss [Member]	Treasury Stock [Member]	Total
Balance at Dec. 31, 2017	$ 99,998	$ 175,651	$ 219,436	$ (1,806)	$ (34,971)	$ 458,308
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	14,808	0	0	14,808
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings, Tax Effect	0	0	1,346	(1,346)	0	0
Other comprehensive income, net of tax	0	0	0	(5,338)	0	(5,338)
Stock options exercised	4	16	0	0	0	20
Cash dividend declared	0	0	(6,323)	0	0	(6,323)
Sale of treasury stock	0	(21)	0	0	615	594
Stock based compensation expense	0	28	0	0	0	28
Balance at Mar. 31, 2018	100,002	175,674	229,267	(8,490)	(34,356)	462,097
Balance at Dec. 31, 2018	100,175	176,710	256,397	(10,309)	(33,102)	489,871
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	14,558	0	0	14,558
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings, Tax Effect				0
Other comprehensive income, net of tax	0	0	0	3,298	0	3,298
Stock options exercised	5	30	0	0	0	35
Cash dividend declared	0	0	(6,591)	0	0	(6,591)
Purchase of treasury stock	0	0	0	0	(35)	(35)
Sale of treasury stock	0	(218)	0	0	812	594
Stock based compensation expense	0	(12)	0	0	0	(12)
Balance at Mar. 31, 2019	$ 100,180	$ 176,510	$ 264,364	$ (7,011)	$ (32,325)	$ 501,718