CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Thousands	Total	Common Stock Class A Common Stock	Common Stock Class B Common Stock	Capital in Excess of Par Value	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balance, beginning of period at Dec. 31, 2018	$ 250,704	$ 5,352	$ 1,569	$ 7,042	$ 250,352	$ (13,611)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	4,924	117		4,807
Purchase of treasury shares	(3,010)	(72)		(2,938)
Net income	39,632				39,632
Cash dividends on common stock	(5,132)				(5,132)
Current period other comprehensive income, net of tax	758					758
Pension settlement, net of tax	671					671
Reclassification adjustment to net income, net of tax	845					845
Balance, end of period at Dec. 31, 2019	289,392	5,397	1,569	8,911	284,852	(11,337)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	3,078	124		2,954
Purchase of treasury shares	(1,002)	(32)		(970)
Conversion of Class B to Class A shares	0	1	(1)
Net income	14,793				14,793
Cash dividends on common stock	(5,375)				(5,375)
Current period other comprehensive income, net of tax	(697)					(697)
Pension settlement, net of tax	0
Reclassification adjustment to net income, net of tax	435					435
Balance, end of period at Dec. 31, 2020	$ 300,624	$ 5,490	$ 1,568	$ 10,895	$ 294,270	$ (11,599)