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Segment Information (Schedule of Revenue by Product and Service) (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
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, 2018
Dec. 31, 2017
Dec. 31, 2016
Revenue $ 180,712 $ 164,511 $ 176,568 $ 165,869 $ 177,264 $ 152,907 $ 159,467 $ 156,431 $ 165,937 $ 156,362 $ 158,111 $ 152,555 $ 687,660 $ 646,069 $ 632,965
Products                              
Revenue                         259,124 222,750 238,011
Materials                              
Revenue                         170,091 168,846 156,839
Services                              
Revenue                         $ 258,445 $ 254,473 $ 238,115