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, 2018	$ 538,898	$ 544	$ 62,239	$ 770,305	$ (137,440)	$ (156,750)
Net income	5,286			5,286
Other comprehensive loss	(2,095)				(2,095)
Comprehensive income (loss)	3,191
Cash dividends declared	(5,734)			(5,734)
Share-based compensation expense	477		477
Delivery of treasury shares
RSUs and PSAs	(322)		(992)			670
Employee stock options exercised — net	(322)		(1,159)			837
Ending Balance at Mar. 31, 2019	536,188	544	60,565	769,857	(139,535)	(155,243)
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 income (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)