Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Capital in Excess of Par Value [Member]	Retained Earnings [Member]	Retained Earnings [Member] Revision of Prior Period, Reclassification, Adjustment [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Other Comprehensive Loss [Member] Revision of Prior Period, Reclassification, Adjustment [Member]	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2017	$ 708,928	$ 544	$ 62,594	$ 948,411	$ 22,298	$ (140,675)	$ (22,298)	$ (161,946)
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201802Member	us-gaap:AccountingStandardsUpdate201802Member	us-gaap:AccountingStandardsUpdate201802Member	us-gaap:AccountingStandardsUpdate201802Member		us-gaap:AccountingStandardsUpdate201802Member		us-gaap:AccountingStandardsUpdate201802Member
Net income (loss)	$ (177,604)			$ (177,604)
Other comprehensive income	25,533					$ 25,533
Comprehensive income (loss)	(152,071)
Tax effect of exercise of stock awards	(7)		$ (7)
Cash dividends declared	(22,800)			(22,800)
Share-based compensation expense	7,000		7,000
Delivery of treasury shares
RSUs and PSAs	(1,626)		(6,201)					$ 4,575
Employee stock options exercised — net	(526)		(1,147)					621
Ending Balance at Dec. 31, 2018	538,898	$ 544	62,239	770,305		(137,440)		(156,750)
Net income (loss)	(21,541)			(21,541)
Other comprehensive income	59,544					59,544
Comprehensive income (loss)	38,003
Cash dividends declared	(22,969)			(22,969)
Share-based compensation expense	3,583		3,583
Delivery of treasury shares
RSUs and PSAs	(792)		(3,625)					2,833
Employee stock options exercised — net	(764)		(2,297)					1,533
Ending Balance at Dec. 31, 2019	555,959	544	59,900	725,795		(77,896)		(152,384)
Net income (loss)	21,298			21,298
Other comprehensive income	19,243					19,243
Comprehensive income (loss)	40,541
Cash dividends declared	(23,728)			(23,728)
Share-based compensation expense	5,655		5,655
Delivery of treasury shares
RSUs and PSAs	(420)		(2,077)					1,657
Employee stock options exercised — net	(75)		(217)					142
Ending Balance at Dec. 31, 2020	$ 577,932	$ 544	$ 63,261	$ 723,365		$ (58,653)		$ (150,585)