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, 2015	$ 419,272	$ 46,249	$ 106,269	$ 390,690	$ (120,104)	$ (3,832)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	37,476			37,476
Other comprehensive income	5,086					5,086
Cash dividends declared	(19,343)			(19,343)
Stock-based compensation expense	1,568		1,568
Restricted awards granted	38		(1,627)		1,665
Exercise of stock options	705		(214)		919
Purchase of treasury shares	(10,018)				(10,018)
Ending balance at Sep. 30, 2016	434,784	46,249	105,996	408,823	(127,538)	1,254
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	44,646			44,646
Other comprehensive income	3,235					3,235
Cash dividends declared	(20,662)			(20,662)
Stock-based compensation expense	1,653		1,653
Restricted awards granted	0		(1,351)		1,351
Issuance of shares of common stock	28,408	1,101	27,307
Exercise of stock options	597		(101)		698
Ending balance at Sep. 30, 2017	$ 500,315	$ 47,619	$ 140,381	$ 441,001	$ (124,909)	$ (3,777)