Segment Information (Schedule Of Revenue From Unaffiliated Customers By Product And Service) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue	$ 165,937	$ 156,362	$ 158,111	$ 152,555	$ 183,363	$ 151,574	$ 170,504	$ 160,722	$ 187,438	$ 166,944	$ 151,512	$ 147,758	$ 632,965	$ 666,163	$ 653,652
Operating Segments [Member] | Products [Member]
Revenue													223,544	257,379	283,339
Operating Segments [Member] | Materials [Member]
Revenue													156,839	150,740	158,859
Operating Segments [Member] | Services [Member]
Revenue													$ 252,582	$ 258,044	$ 211,454