Consolidated 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, 2016	$ 653,826	$ 544	$ 57,917	$ 962,884	$ (204,606)	$ (162,913)
Previously unrecognized excess tax benefit on exercise of stock awards	317			317
Net income (loss)	7,914			7,914
Other comprehensive income	63,931				63,931
Comprehensive income (loss)	71,845
Cash dividends declared	(22,704)			(22,704)
Share-based compensation expense	6,214		6,214
Delivery of treasury shares
RSUs and PSAs	(114)		(535)			421
Employee stock options exercised — net	(456)		(1,002)			546
Ending Balance at Dec. 31, 2017	708,928	544	62,594	948,411	(140,675)	(161,946)
Reclassification pursuant to ASU No. 2018-02				22,298	(22,298)
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)