Goodwill and Intangible Assets - Schedule of Changes in Carrying Amount of Goodwill (Details) $ in Thousands	9 Months Ended
Sep. 30, 2018 USD ($)
Goodwill [Roll Forward]
Balance at December 31, 2017	$ 1,704,158
Foreign currency translation	(8,447)
Acquisitions	11,920
Acquisition adjustments	1,152
Balance at September 30, 2018	1,708,783
FMT
Goodwill [Roll Forward]
Balance at December 31, 2017	586,064
Foreign currency translation	(2,423)
Acquisitions	0
Acquisition adjustments	0
Balance at September 30, 2018	583,641
HST
Goodwill [Roll Forward]
Balance at December 31, 2017	740,032
Foreign currency translation	(2,765)
Acquisitions	11,920
Acquisition adjustments	1,152
Balance at September 30, 2018	750,339
FSDP
Goodwill [Roll Forward]
Balance at December 31, 2017	378,062
Foreign currency translation	(3,259)
Acquisitions	0
Acquisition adjustments	0
Balance at September 30, 2018	$ 374,803

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of increase (decrease) of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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