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, 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)	(1,683)			(1,683)
Other comprehensive income (loss)	(11,633)				(11,633)
Comprehensive income (loss)	(13,316)
Cash dividends declared	(11,383)			(11,383)
Share-based compensation expense	3,704		3,704
Delivery of treasury shares
RSUs and PSAs	(476)		(2,376)			1,900
Employee stock options exercised — net	(505)		(1,095)			590
Ending Balance at Jun. 30, 2018	686,952	544	62,827	957,643	(174,606)	(159,456)
Beginning Balance at Mar. 31, 2018	723,992	544	62,359	970,736	(148,953)	(160,694)
Net income (loss)	(7,399)			(7,399)
Other comprehensive income (loss)	(25,653)				(25,653)
Comprehensive income (loss)	(33,052)
Cash dividends declared	(5,694)			(5,694)
Share-based compensation expense	1,722		1,722
Delivery of treasury shares
RSUs and PSAs	(1)		(1,216)			1,215
Employee stock options exercised — net	(15)		(38)			23
Ending Balance at Jun. 30, 2018	686,952	544	62,827	957,643	(174,606)	(159,456)
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)