Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Capital in Excess of Par Value [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2019	$ 555,959	$ 544	$ 59,900	$ 725,795	$ (77,896)	$ (152,384)
Net income	7,406			7,406
Other comprehensive loss	(15,321)				(15,321)
Comprehensive loss	(7,915)
Cash dividends declared	(5,761)			(5,761)
Share-based compensation expense	1,085		1,085
Delivery of treasury shares
RSUs and PSAs	(406)		(1,213)			807
Employee stock options exercised — net	(52)		(149)			97
Ending Balance at Mar. 31, 2020	542,910	544	59,623	727,440	(93,217)	(151,480)
Beginning Balance at Dec. 31, 2020	577,932	544	63,261	723,365	(58,653)	(150,585)
Net income	8,394			8,394
Other comprehensive loss	(9,840)				(9,840)
Comprehensive loss	(1,446)
Cash dividends declared	(6,003)			(6,003)
Share-based compensation expense	1,208		1,208
Delivery of treasury shares
RSUs and PSAs	(630)		(1,893)			1,263
Ending Balance at Mar. 31, 2021	$ 571,061	$ 544	$ 62,576	$ 725,756	$ (68,493)	$ (149,322)