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 (loss)	11,117			11,117
Other comprehensive income (loss)	3,704				3,704
Comprehensive income (loss)	14,821
Cash dividends declared	(11,482)			(11,482)
Share-based compensation expense	1,638		1,638
Delivery of treasury shares
RSUs and PSAs	(324)		(2,421)			2,097
Employee stock options exercised — net	(432)		(1,536)			1,104
Ending Balance at Jun. 30, 2019	543,119	544	59,920	769,940	(133,736)	(153,549)
Beginning Balance at Mar. 31, 2019	536,188	544	60,565	769,857	(139,535)	(155,243)
Net income (loss)	5,831			5,831
Other comprehensive income (loss)	5,799				5,799
Comprehensive income (loss)	11,630
Cash dividends declared	(5,748)			(5,748)
Share-based compensation expense	1,161		1,161
Delivery of treasury shares
RSUs and PSAs	(2)		(1,429)			1,427
Employee stock options exercised — net	(110)		(377)			267
Ending Balance at Jun. 30, 2019	543,119	544	59,920	769,940	(133,736)	(153,549)
Beginning Balance at Dec. 31, 2019	555,959	544	59,900	725,795	(77,896)	(152,384)
Net income (loss)	4,990			4,990
Other comprehensive income (loss)	(10,081)				(10,081)
Comprehensive income (loss)	(5,091)
Cash dividends declared	(11,750)			(11,750)
Share-based compensation expense	2,377		2,377
Delivery of treasury shares
RSUs and PSAs	(421)		(2,078)			1,657
Employee stock options exercised — net	(75)		(217)			142
Ending Balance at Jun. 30, 2020	540,999	544	59,982	719,035	(87,977)	(150,585)
Beginning Balance at Mar. 31, 2020	542,910	544	59,623	727,440	(93,217)	(151,480)
Net income (loss)	(2,416)			(2,416)
Other comprehensive income (loss)	5,240				5,240
Comprehensive income (loss)	2,824
Cash dividends declared	(5,989)			(5,989)
Share-based compensation expense	1,292		1,292
Delivery of treasury shares
RSUs and PSAs	(15)		(865)			850
Employee stock options exercised — net	(23)		(68)			45
Ending Balance at Jun. 30, 2020	$ 540,999	$ 544	$ 59,982	$ 719,035	$ (87,977)	$ (150,585)