Goodwill and Other Intangible Assets - Rollforward of Other Intangible Assets (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Other Intangible Assets [Line Items]
Other intangible assets, gross		$ 432,600
Accumulated amortization		(248,600)
Other Intangible Assets [Rollforward]
Other intangible assets, net, beginning balance	$ 184,043
Additions from new business combinations	367,200
Currency translation adjustments	300
Amortization expense	(54,500)
Other intangible assets, net, ending balance	496,963
Customer Relationships and Backlog
Other Intangible Assets [Line Items]
Other intangible assets, amortizing, gross		297,900
Accumulated amortization		(218,500)
Other Intangible Assets [Rollforward]
Other intangible assets, net, amortizing, beginning balance	79,400
Additions from new business combinations, amortizing intangible assets	311,800
Currency translation adjustments, amortizing intangible assets	0
Amortization expense	(41,500)
Other intangible assets, net, amortizing, ending balance	349,700
Pre-Qualifications
Other Intangible Assets [Line Items]
Other intangible assets, amortizing, gross		73,800
Accumulated amortization		(10,600)
Other Intangible Assets [Rollforward]
Other intangible assets, net, amortizing, beginning balance	63,200
Additions from new business combinations, amortizing intangible assets	0
Currency translation adjustments, amortizing intangible assets	300
Amortization expense	(8,400)
Other intangible assets, net, amortizing, ending balance	55,100
Other
Other Intangible Assets [Line Items]
Other intangible assets, amortizing, gross		26,400
Accumulated amortization		(19,500)
Other Intangible Assets [Rollforward]
Other intangible assets, net, amortizing, beginning balance	6,900
Additions from new business combinations, amortizing intangible assets	55,400
Currency translation adjustments, amortizing intangible assets	0
Amortization expense	(4,600)
Other intangible assets, net, amortizing, ending balance	57,700
Trade Names
Other Intangible Assets [Line Items]
Other intangible assets, non-amortizing	34,500	$ 34,500
Other Intangible Assets [Rollforward]
Other intangible assets, non-amortizing, beginning balance	34,500
Additions from new business combinations, non-amortizing intangible assets	0
Currency translation adjustments, non-amortizing intangible assets	0
Other intangible assets, non-amortizing, ending balance	$ 34,500