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 (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)
Beginning Balance at Dec. 31, 2020	577,932	544	63,261	723,365	(58,653)	(150,585)
Net income (loss)	9,804			9,804
Other comprehensive income (loss)	(6,160)				(6,160)
Comprehensive income (loss)	3,644
Cash dividends declared	(12,235)			(12,235)
Share-based compensation expense	2,537		2,537
Delivery of treasury shares
RSUs and PSAs	(633)		(3,002)			2,369
Ending Balance at Jun. 30, 2021	571,245	544	62,796	720,934	(64,813)	(148,216)
Beginning Balance at Mar. 31, 2021	571,061	544	62,576	725,756	(68,493)	(149,322)
Net income (loss)	1,410			1,410
Other comprehensive income (loss)	3,680				3,680
Comprehensive income (loss)	5,090
Cash dividends declared	(6,232)			(6,232)
Share-based compensation expense	1,329		1,329
Delivery of treasury shares
RSUs and PSAs	(3)		(1,109)			1,106
Ending Balance at Jun. 30, 2021	$ 571,245	$ 544	$ 62,796	$ 720,934	$ (64,813)	$ (148,216)