Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Capital Stock [Member]	Surplus [Member]	Undivided Profits [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Treasury Stock [Member]	Total
Balance at Dec. 31, 2016	$ 99,214	$ 171,425	$ 201,517	$ (6,251)	$ (33,219)	$ 432,686
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	10,947	0	0	10,947
Other comprehensive income, net of tax	0	0	0	683	0	683
Stock options exercised	279	1,224	0	0	0	1,503
Cash dividend declared	0	0	(6,291)	0	0	(6,291)
Purchase of treasury stock	0	0	0	0	(1,503)	(1,503)
Sale of treasury stock	0	(63)	0	0	696	633
Stock based compensation expense	0	42	0	0	0	42
Balance at Mar. 31, 2017	99,493	172,628	206,173	(5,568)	(34,026)	438,700
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