Goodwill and Intangible Assets - Schedule of Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill		$ 1,980,376
Accumulated goodwill impairment losses		(200,631)
Goodwill [Roll Forward]
Balance at December 31, 2019	$ 1,779,745
Foreign currency translation	20,295
Acquisitions	61,739
Acquisition adjustments	1,798
Balance at September 30, 2020	1,863,577
FMT
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill		599,646
Accumulated goodwill impairment losses		(20,721)
Goodwill [Roll Forward]
Balance at December 31, 2019	578,925
Foreign currency translation	4,726
Acquisitions	61,739
Acquisition adjustments	0
Balance at September 30, 2020	645,390
HST
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill		981,592
Accumulated goodwill impairment losses		(149,820)
Goodwill [Roll Forward]
Balance at December 31, 2019	831,772
Foreign currency translation	9,832
Acquisitions	0
Acquisition adjustments	1,798
Balance at September 30, 2020	843,402
FSDP
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill		399,138
Accumulated goodwill impairment losses		$ (30,090)
Goodwill [Roll Forward]
Balance at December 31, 2019	369,048
Foreign currency translation	5,737
Acquisitions	0
Acquisition adjustments	0
Balance at September 30, 2020	$ 374,785