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, 2014	$ 649,109	$ 544	$ 54,342	$ 919,468	$ (154,870)	$ (170,375)
Net income	64,575			64,575
Other comprehensive income (loss)	(35,616)				(35,616)
Comprehensive income	28,959
Tax effect on exercise of stock awards	843		843
Cash dividends declared	(20,900)			(20,900)
Share-based compensation expense	4,403		4,403
Delivery of treasury shares
RSUs and PSAs	(1,976)		(5,078)			3,102
401 (k) plans	2,848		838			2,010
Employee stock options exercised — net	(39)		(436)			397
Ending Balance at Dec. 31, 2015	663,247	544	54,912	963,143	(190,486)	(164,866)
Net income	21,554			21,554
Other comprehensive income (loss)	(14,120)				(14,120)
Comprehensive income	7,434
Tax effect on exercise of stock awards	58		58
Cash dividends declared	(21,813)			(21,813)
Share-based compensation expense	5,889		5,889
Delivery of treasury shares
RSUs and PSAs	(751)		(2,375)			1,624
Employee stock options exercised — net	(238)		(567)			329
Ending Balance at Dec. 31, 2016	653,826	544	57,917	962,884	(204,606)	(162,913)
Previously unrecognized excess tax benefit onexercise of stock awards	317			317
Net income	7,914			7,914
Other comprehensive income (loss)	63,931				63,931
Comprehensive income	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)