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, 2017	$ 197	$ 347,691	$ 96,547	$ (296)	$ (14,939)	$ 429,200
Increase (Decrease) in Stockholders' Equity
Net income			25,363			25,363
Shares issued under the dividend reinvestment plan		705				705
Stock awards granted and distributed	1	(529)		528
Stock awards forfeited		183		(183)
Repurchase of surrendered stock from vesting of stock plans				(569)		(569)
Share based compensation expense		2,689				2,689
Cash dividend declared			(13,749)			(13,749)
Other comprehensive loss, net of deferred income taxes					(3,654)	(3,654)
Balance at Sep. 30, 2018	198	350,739	108,161	(520)	(18,593)	439,985
Balance at Jun. 30, 2018	198	349,538	106,206	(441)	(15,746)	439,755
Increase (Decrease) in Stockholders' Equity
Net income			6,547			6,547
Shares issued under the dividend reinvestment plan		237				237
Stock awards granted and distributed		(6)		6
Stock awards forfeited		68		(68)
Repurchase of surrendered stock from vesting of stock plans				(17)		(17)
Share based compensation expense		902				902
Cash dividend declared			(4,592)			(4,592)
Other comprehensive loss, net of deferred income taxes					(2,847)	(2,847)
Balance at Sep. 30, 2018	198	350,739	108,161	(520)	(18,593)	439,985
Balance at Dec. 31, 2018	198	352,093	117,432	(781)	(15,112)	453,830
Increase (Decrease) in Stockholders' Equity
Net income			37,483			37,483
Shares issued under the dividend reinvestment plan		643				643
Shares issued under the Employee Stock Purchase Plan		122				122
Purchase of treasury stock				(625)		(625)
Stock awards granted and distributed	1	(988)		987
Stock awards forfeited		479		(479)
Repurchase of surrendered stock from vesting of stock plans		(18)		(859)		(877)
Share based compensation expense		2,755				2,755
Cash dividend declared			(13,812)			(13,812)
Other comprehensive loss, net of deferred income taxes					6,884	6,884
Balance at Sep. 30, 2019	199	355,086	141,103	(1,757)	(8,228)	486,403
Balance at Jun. 30, 2019	199	353,729	131,811	(1,337)	(9,197)	475,205
Increase (Decrease) in Stockholders' Equity
Net income			13,903			13,903
Shares issued under the dividend reinvestment plan		224				224
Shares issued under the Employee Stock Purchase Plan		122				122
Purchase of treasury stock				(304)		(304)
Stock awards granted and distributed		(33)		33
Stock awards forfeited		137		(137)
Repurchase of surrendered stock from vesting of stock plans				(12)		(12)
Share based compensation expense		907				907
Cash dividend declared			(4,611)			(4,611)
Other comprehensive loss, net of deferred income taxes					969	969
Balance at Sep. 30, 2019	$ 199	$ 355,086	$ 141,103	$ (1,757)	$ (8,228)	$ 486,403