Selected Income Statement Information Selected Income Statement Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue:
Services	$ 1,245,927	$ 1,181,229	$ 1,509,786
Products	663,555	740,278	761,817
Total revenue	1,909,482	1,921,507	2,271,603
Cost of Services and Products:
Services	1,135,084	1,040,817	1,330,218
Products	578,212	625,843	615,438
Unallocated expenses	66,960	60,237	46,720
Total cost of services and products	1,780,256	1,726,897	1,992,376
Gross margin:
Services	110,843	140,412	179,568
Products	85,343	114,435	146,379
Unallocated expenses	(66,960)	(60,237)	(46,720)
Gross Margin	$ 129,226	$ 194,610	$ 279,227