Consolidated Statements of Changes in Stockholders Equity (Uaudited) - USD ($) $ in Thousands	Total	Common Stock	Capital in Excess of Par Value	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock
Beginning Balance at Dec. 31, 2015	$ 580,471	$ 560	$ 256,435	$ 696	$ 570,630	$ (247,850)
Beginning Balance (in shares) at Dec. 31, 2015		55,945,245
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	15,770				15,770
Other comprehensive income	10,758			10,758
Cash dividend	(1,783)				(1,783)
Issuance of common stock including proceeds from exercise of common stock options	660	$ 1	659
Issuance of common stock including proceeds from exercise of common stock options (in shares)		61,498
Stock-based compensation expense	699		699
Repurchase of common stock	(8,995)					(8,995)
Ending Balance at Mar. 31, 2016	597,580	$ 561	257,793	11,454	584,617	(256,845)
Ending Balance (in shares) at Mar. 31, 2016		56,006,743
Beginning Balance at Dec. 31, 2016	687,336	$ 580	329,457	(7,617)	627,078	(262,162)
Beginning Balance (in shares) at Dec. 31, 2016		55,995,219
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	18,937				18,937
Other comprehensive income	830			830
Cash dividend	(2,199)				(2,199)
Issuance of common stock including proceeds from exercise of common stock options	1,094	$ 1	1,093
Issuance of common stock including proceeds from exercise of common stock options (in shares)		129,781
Stock-based compensation expense	821		821
Repurchase of common stock	(2,818)					(2,818)
Ending Balance at Mar. 31, 2017	$ 704,001	$ 581	$ 331,371	$ (6,787)	$ 643,816	$ (264,980)
Ending Balance (in shares) at Mar. 31, 2017		56,125,000