Consolidated Statements of Stockholders' Equity (unaudited) - USD ($) $ in Thousands	Common Stock	Surplus	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Loss	Total
Balance at Dec. 31, 2018	$ 198	$ 352,093	$ 117,432	$ (781)	$ (15,112)	$ 453,830
Increase (Decrease) in Stockholders' Equity
Net income			12,927			12,927
Shares issued under the dividend reinvestment plan		198				198
Stock awards granted and distributed	1	(791)		790
Repurchase of surrendered stock from vesting of stock plans				795		795
Share based compensation expense		954				954
Cash dividend declared			(4,594)			(4,594)
Other comprehensive income (loss), net of deferred income taxes					2,483	2,483
Balance at Mar. 31, 2019	199	352,454	125,765	(786)	(12,629)	465,003
Increase (Decrease) in Stockholders' Equity
Cumulative change in accounting principle (Note 1)			(1,473)			(1,473)
Balance at January 1, 2020 (as adjusted for change in accounting principle)	199	356,436	149,230	(1,843)	(8,341)	495,681
Balance at Dec. 31, 2019	199	356,436	150,703	(1,843)	(8,341)	497,154
Increase (Decrease) in Stockholders' Equity
Net income			9,348			9,348
Shares issued under the dividend reinvestment plan		240				240
Purchase of treasury stock				(4,633)		(4,633)
Stock awards granted and distributed		(2,668)		2,668
Stock awards forfeited		20		(20)
Repurchase of surrendered stock from vesting of stock plans		36		972		1,008
Share based compensation expense		1,022				1,022
Cash dividend declared			(4,812)			(4,812)
Other comprehensive income (loss), net of deferred income taxes					(2,585)	(2,585)
Balance at Mar. 31, 2020	$ 199	$ 355,014	$ 153,766	$ (4,800)	$ (10,926)	$ 493,253