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	16,026			16,026
Other comprehensive income	873					873
Cash dividends declared	(6,917)			(6,917)
Stock-based compensation expense	780		780
Restricted awards granted	0		(638)		638
Issuance of shares of common stock	28,408	1,101	27,307
Exercise of stock options	38		(17)		55
Ending balance at Mar. 31, 2017	481,646	47,619	140,305	426,126	(126,265)	(6,139)
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	17,616			17,616
Other comprehensive income	(8,218)					(8,218)
Adoption of new accounting pronouncement (see Note B)	0
Adoption of new accounting pronouncement (see Note B) | Accounting Standards Update 2016-01				2,657		(2,657)
Cash dividends declared	(7,104)			(7,104)
Stock-based compensation expense	793		793
Restricted awards granted	0		(1,135)		1,135
Exercise of stock options	280		(71)		351
Purchase of treasury shares	(13,997)				(13,997)
Ending balance at Mar. 31, 2018	$ 491,877	$ 47,619	$ 140,547	$ 457,650	$ (137,420)	$ (16,519)