Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Capital Stock [Member]	Surplus [Member]	Undivided Profits [Member]	Accumulated Other Comprehensive Income [Member]	Treasury Stock [Member]	Total
Balance at Dec. 31, 2019	$ 100,205	$ 176,427	$ 288,067	$ 4,461	$ (30,903)	$ 538,257
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	13,313	0	0	13,313
Other comprehensive income (loss), net of tax	0	0	0	6,931	0	6,931
Cash dividend declared	0	0	(6,827)	0	0	(6,827)
Purchase of treasury stock	0	0	0	0	(3,493)	(3,493)
Stock based compensation expense	0	4	0	0	0	4
Balance at Mar. 31, 2020	100,205	176,431	294,553	11,392	(34,396)	548,185
Balance at Dec. 31, 2020	100,205	176,442	313,974	11,936	(34,396)	568,161
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	14,083	0	0	14,083
Other comprehensive income (loss), net of tax	0	0	0	(4,668)	0	(4,668)
Stock options exercised	13	58	0	0	0	71
Cash dividend declared	0	0	(6,571)	0	0	(6,571)
Purchase of treasury stock	0	0	0	0	(45)	(45)
Balance at Mar. 31, 2021	$ 100,218	$ 176,500	$ 321,486	$ 7,268	$ (34,441)	$ 571,031