Segment Information (Schedule Of Revenue From Unaffiliated Customers By Product And Service) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue	$ 177,264	$ 152,907	$ 159,467	$ 156,431	$ 165,937	$ 156,362	$ 158,111	$ 152,555	$ 183,363	$ 151,574	$ 170,504	$ 160,722	$ 646,069	$ 632,965	$ 666,163
Operating Segments [Member] | Products [Member]
Revenue													210,280	223,544	257,379
Operating Segments [Member] | Materials [Member]
Revenue													168,846	156,839	150,740
Operating Segments [Member] | Services [Member]
Revenue													$ 266,943	$ 252,582	$ 258,044