Unaudited Condensed Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Total Stockholders' Equity	Common Stock Shares Outstanding Class A	Common Stock Shares Outstanding Class B	Capital in Excess of Par Value	Retained Earnings	Foreign Currency Translation Adjustment	Deferred Gain (Loss) on Available for Sale Securities	Deferred Gain (Loss) on Cash Flow Hedging	Pension and Postretirement Plan Adjustment
Balance, beginning of period at Dec. 31, 2015		$ 201,138	$ 5,265	$ 1,572	$ 0	$ 217,745	$ (5,455)	$ 1,480	$ (112)	$ (19,357)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation		1,505	46		1,459
Purchase of treasury shares		(3,826)	(70)		(1,459)	(2,297)
Net income	$ 5,918	5,918				5,918
Cash dividends on Class A and Class B common stock		(3,638)				(3,638)
Current period other comprehensive income (loss)		(2,535)					(818)	164	(1,881)
Reclassification adjustment to net income		410							108	302
Balance, end of period at Jun. 30, 2016		198,972	5,241	1,572	0	217,728	(6,273)	1,644	(1,885)	(19,055)
Balance, beginning of period at Dec. 31, 2016		220,293	5,208	1,571	0	239,441	(7,533)	1,893	393	(20,680)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation		779	57		0	722
Conversion of Class B to Class A shares	0		1	(1)
Net income	$ 11,766	11,766				11,766
Cash dividends on Class A and Class B common stock		(3,690)				(3,690)
Current period other comprehensive income (loss)		1,348					1,743	464	(859)
Reclassification adjustment to net income		464							140	324
Balance, end of period at Jun. 30, 2017		$ 230,960	$ 5,266	$ 1,570	$ 0	$ 248,239	$ (5,790)	$ 2,357	$ (326)	$ (20,356)