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)
Reclassisfication pursuant to ASU No. 2018-02				22,298	(22,298)
Net income	5,716			5,716
Other comprehensive income (loss)	14,020				14,020
Comprehensive income	19,736
Cash dividends declared	(5,689)			(5,689)
Share-based compensation expense	1,982		1,982
Delivery of treasury shares
RSUs and PSAs	(475)		(1,160)			685
Employee stock options exercised — net	(490)		(1,057)			567
Ending Balance at Mar. 31, 2018	723,992	544	62,359	970,736	(148,953)	(160,694)
Beginning Balance at Dec. 31, 2018	538,898	544	62,239	770,305	(137,440)	(156,750)
Net income	5,286			5,286
Other comprehensive income (loss)	(2,095)				(2,095)
Comprehensive income	3,191
Cash dividends declared	(5,734)			(5,734)
Share-based compensation expense	477		477
Delivery of treasury shares
RSUs and PSAs	(322)		(992)			670
Employee stock options exercised — net	(322)		(1,159)			837
Ending Balance at Mar. 31, 2019	$ 536,188	$ 544	$ 60,565	$ 769,857	$ (139,535)	$ (155,243)