Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock Cumulative Effect, Period of Adoption, Adjusted Balance	Common Stock	Surplus Cumulative Effect, Period of Adoption, Adjusted Balance	Surplus	Retained Earnings Effect of adoption	Retained Earnings Cumulative Effect, Period of Adoption, Adjusted Balance	Retained Earnings	Treasury Stock Cumulative Effect, Period of Adoption, Adjusted Balance	Treasury Stock	Accumulated Other Comprehensive Loss Cumulative Effect, Period of Adoption, Adjusted Balance	Accumulated Other Comprehensive Loss	Effect of adoption	Cumulative Effect, Period of Adoption, Adjusted Balance	Total
Balance at Dec. 31, 2017		$ 197		$ 347,691			$ 96,547		$ (296)		$ (14,939)			$ 429,200
Increase (Decrease) in Stockholders' Equity
Net income							39,227							39,227
Shares issued under the dividend reinvestment plan ("DRP")				954										954
Shares issued under the Employee Stock Purchase Plan ("ESPP")				63										63
Stock awards granted and distributed		1		(539)					538
Stock awards forfeited				437					(437)
Repurchase of surrendered stock from vesting of stock plans									586					586
Share based compensation expense				3,487										3,487
Cash dividend declared							(18,342)							(18,342)
Other comprehensive (loss) income, net of deferred income taxes											(173)			(173)
Balance at Dec. 31, 2018		198		352,093			117,432		(781)		(15,112)			453,830
Increase (Decrease) in Stockholders' Equity
Net income							51,691							51,691
Shares issued under the dividend reinvestment plan ("DRP")				867										867
Shares issued under the Employee Stock Purchase Plan ("ESPP")				235										235
Purchase of treasury stock									(625)					(625)
Stock awards granted and distributed		1		(988)					987
Stock awards forfeited				555					(555)
Repurchase of surrendered stock from vesting of stock plans				18					869					887
Share based compensation expense				3,692										3,692
Cash dividend declared							(18,420)							(18,420)
Other comprehensive (loss) income, net of deferred income taxes											6,771			6,771
Balance at Dec. 31, 2019	$ 199	199	$ 356,436	356,436	$ (1,473)	$ 149,230	150,703	$ (1,843)	(1,843)	$ (8,341)	(8,341)	$ (1,473)	$ 495,681	497,154
Increase (Decrease) in Stockholders' Equity
Net income							42,042							42,042
Shares issued under the dividend reinvestment plan ("DRP")				1,012										1,012
Shares issued under the Employee Stock Purchase Plan ("ESPP")				255										255
Purchase of treasury stock									(4,633)					(4,633)
Stock awards granted and distributed				(4,167)					4,167
Stock awards forfeited				222					(222)
Repurchase of surrendered stock from vesting of stock plans				656					2,525					3,181
Share based compensation expense				7,639										7,639
Cash dividend declared							(19,197)							(19,197)
Other comprehensive (loss) income, net of deferred income taxes											(1,787)			(1,787)
Balance at Dec. 31, 2020		$ 199		$ 360,741			$ 172,075		$ (5,056)		$ (10,128)			$ 517,831