Goodwill and Other Intangible Assets (Rollforward of Other Intangible Assets) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 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	52,300
Currency translation adjustments	500
Amortization expense	(11,200)
Other intangible assets, net, ending balance	225,566
Customer Relationships and Backlog [Member]
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	48,000
Currency translation adjustments, amortizing intangible assets	0
Amortization expense	(7,900)
Other intangible assets, net, amortizing, ending balance	119,500
Pre-Qualifications [Member]
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	500
Amortization expense	(2,700)
Other intangible assets, net, amortizing, ending balance	61,000
Other Amortizing Intangible Assets [Member]
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	4,300
Currency translation adjustments, amortizing intangible assets	0
Amortization expense	(600)
Other intangible assets, net, amortizing, ending balance	10,600
Trade Names [Member]
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