Goodwill and Intangible Assets - Schedule of Changes in Carrying Amount of Goodwill (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill		$ 2,096,205
Accumulated goodwill impairment losses		(200,631)
Goodwill [Roll Forward]
Balance at December 31, 2020	$ 1,895,574
Foreign currency translation	(28,705)
Acquisitions	330,749
Disposition of businesses	(129)
Acquisition adjustments	(405)
Balance at September 30, 2021	2,197,084
FMT
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill		670,442
Accumulated goodwill impairment losses		(20,721)
Goodwill [Roll Forward]
Balance at December 31, 2020	649,721
Foreign currency translation	(7,132)
Acquisitions	59,481
Disposition of businesses	0
Acquisition adjustments	(405)
Balance at September 30, 2021	701,665
HST
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill		1,012,448
Accumulated goodwill impairment losses		(149,820)
Goodwill [Roll Forward]
Balance at December 31, 2020	862,628
Foreign currency translation	(14,168)
Acquisitions	271,268
Disposition of businesses	(129)
Acquisition adjustments	0
Balance at September 30, 2021	1,119,599
FSDP
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill		413,315
Accumulated goodwill impairment losses		$ (30,090)
Goodwill [Roll Forward]
Balance at December 31, 2020	383,225
Foreign currency translation	(7,405)
Acquisitions	0
Disposition of businesses	0
Acquisition adjustments	0
Balance at September 30, 2021	$ 375,820