Consolidated Statements Of Changes In Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Capital Surplus[Member]	Retained Earnings [Member]	Treasury Stock, Common [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning balance at Dec. 31, 2014	$ 390,853	$ 46,249	$ 107,370	$ 362,211	$ (120,818)	$ (4,159)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income Available to Common Shareholders	54,097			54,097
Other comprehensive income	327					327
Cash dividends declared	(25,618)			(25,618)
Stock-based compensation expense, net	1,456		1,456
Restricted Awards Granted	337		(1,190)		1,527
Exercise of stock options	2,979		(602)		3,581
Stock issued during period, value, other	1,896		(765)		2,661
Purchase of treasury shares	(7,055)				(7,055)
Ending balance at Dec. 31, 2015	419,272	46,249	106,269	390,690	(120,104)	(3,832)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income Available to Common Shareholders	52,128			52,128
Other comprehensive income	(3,180)					(3,180)
Cash dividends declared	(25,801)			(25,801)
Stock-based compensation expense, net	1,979		1,979
Restricted Awards Granted	39		(1,706)		1,745
Stock issued during period, value, new issues	6,864	269	6,595
Exercise of stock options	1,155		(264)		1,419
Purchase of treasury shares	(10,018)				(10,018)
Ending balance at Dec. 31, 2016	442,438	46,518	112,873	417,017	(126,958)	(7,012)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income Available to Common Shareholders	54,310			54,310
Other comprehensive income	2,367					2,367
ReclasificationofResidualtTaxImpactofTaxRateChange	0			999		(999)
Cash dividends declared	(27,845)			(27,845)
Stock-based compensation expense, net	2,097		2,097
Restricted Awards Granted	0		(1,351)		1,351
Stock issued during period, value, new issues	28,408	1,101	27,307
Exercise of stock options	732		34		698
Ending balance at Dec. 31, 2017	$ 502,507	$ 47,619	$ 140,960	$ 444,481	$ (124,909)	$ (5,644)