Consolidated Statements Of Changes In Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Capital Surplus	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)
Beginning 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	30,714			30,714
Other comprehensive income	2,927					2,927
Cash dividends declared	(13,787)			(13,787)
Stock-based compensation expense	1,210		1,210
Restricted awards granted	0		(1,317)		1,317
Issuance of shares of common stock	28,408	1,101	27,307
Exercise of stock options	597		(101)		698
Ending balance at Jun. 30, 2017	492,507	47,619	139,972	433,944	(124,943)	(4,085)
Beginning Balance at Dec. 31, 2017	502,507	47,619	140,960	444,481	(124,909)	(5,644)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	38,590			38,590
Other comprehensive income	(10,650)					(10,650)
Adoption of new accounting pronouncement (see Note B)	0					(2,657)
Adoption of new accounting pronouncement (see Note B) | Accounting Standards Update 2016-01	(2,700)			2,657		(2,657)
Cash dividends declared	(14,213)			(14,213)
Stock-based compensation expense	1,242		1,242
Restricted awards granted	0		(1,494)		1,494
Exercise of stock options	968		(617)		1,585
Purchase of treasury shares	(14,690)				(14,690)
Ending balance at Jun. 30, 2018	$ 503,754	$ 47,619	$ 140,091	$ 471,515	$ (136,520)	$ (18,951)