Goodwill and Intangible Assets - Schedule of Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill		$ 1,898,586
Accumulated goodwill impairment losses		(200,631)
Goodwill [Roll Forward]
Balance at December 31, 2018	$ 1,697,955
Foreign currency translation	(21,100)
Acquisitions	97,352
Acquisition adjustments	183
Balance at September 30, 2019	1,774,390
FMT
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill		601,762
Accumulated goodwill impairment losses		(20,721)
Goodwill [Roll Forward]
Balance at December 31, 2018	581,041
Foreign currency translation	(4,797)
Acquisitions	0
Acquisition adjustments	0
Balance at September 30, 2019	576,244
HST
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill		895,177
Accumulated goodwill impairment losses		(149,820)
Goodwill [Roll Forward]
Balance at December 31, 2018	745,357
Foreign currency translation	(10,083)
Acquisitions	97,352
Acquisition adjustments	183
Balance at September 30, 2019	832,809
FSDP
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill		401,647
Accumulated goodwill impairment losses		$ (30,090)
Goodwill [Roll Forward]
Balance at December 31, 2018	371,557
Foreign currency translation	(6,220)
Acquisitions	0
Acquisition adjustments	0
Balance at September 30, 2019	$ 365,337