Goodwill and Other Intangible Assets (Rollforward of Other Intangible Assets) (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2017
Other Intangible Assets [Line Items]
Other intangible assets, gross						$ 356,900
Accumulated amortization						(165,800)
Other Intangible Assets [Roll Forward]
Other intangible assets, net, beginning balance			$ 169,370	$ 191,100
Additions from new business combinations			73,100	3,600
Measurement period adjustments			(6,900)	(700)
Intangible asset impairment, non-amortizing intangible assets			(3,300)
Intangible asset impairment			(3,300)
Amortization expense			(23,000)	(20,600)	$ (20,900)
Currency translation adjustments			2,200	(4,000)
Other intangible assets, net, amortizing, ending balance	$ 104,100	$ 104,100	104,100
Other intangible assets, net, ending balance	$ 211,528	211,528	211,528	169,370	191,100
Weighted Average [Member]
Other Intangible Assets [Roll Forward]
Remaining weighted average amortization period (in years)	9 years
Customer Relationships and Backlog [Member]
Other Intangible Assets [Line Items]
Other intangible assets, amortizing, gross						223,000
Accumulated amortization						(152,400)
Other Intangible Assets [Roll Forward]
Other intangible assets, net, amortizing, beginning balance			54,400	70,600
Additions from new business combinations, amortizing intangible assets			67,700	3,300
Measurement period adjustments, amortizing intangible assets			(6,700)	0
Intangible asset impairment, amortizing intangible assets			0
Amortization expense			(20,200)	(19,200)
Currency translation adjustments, amortizing intangible assets			100	(300)
Other intangible assets, net, amortizing, ending balance	$ 95,300	95,300	95,300	54,400	70,600
Customer Relationships and Backlog [Member] | Weighted Average [Member]
Other Intangible Assets [Roll Forward]
Remaining weighted average amortization period (in years)	9 years
Other Amortizing Intangible Assets [Member]
Other Intangible Assets [Line Items]
Other intangible assets, amortizing, gross						21,800
Accumulated amortization						(13,400)
Other Intangible Assets [Roll Forward]
Other intangible assets, net, amortizing, beginning balance			6,500	8,400
Additions from new business combinations, amortizing intangible assets			5,200	300
Measurement period adjustments, amortizing intangible assets			(200)	(700)
Intangible asset impairment, amortizing intangible assets			0
Amortization expense			(2,800)	(1,400)
Currency translation adjustments, amortizing intangible assets			100	(100)
Other intangible assets, net, amortizing, ending balance	$ 8,800	8,800	8,800	6,500	8,400
Other Amortizing Intangible Assets [Member] | Weighted Average [Member]
Other Intangible Assets [Roll Forward]
Remaining weighted average amortization period (in years)	6 years
Trade Names [Member]
Other Intangible Assets [Line Items]
Other intangible assets, non-amortizing	$ 34,500	34,500	34,500	34,500	34,500	34,500
Other Intangible Assets [Roll Forward]
Other intangible assets, non-amortizing, beginning balance			34,500	34,500
Additions from new business combinations, non-amortizing intangible assets			0	0
Measurement period adjustments, non-amortizing intangible assets			0	0
Intangible asset impairment, non-amortizing intangible assets			0
Currency translation adjustments, non-amortizing intangible assets			0	0
Other intangible assets, non-amortizing, ending balance	34,500	34,500	34,500	34,500	34,500
Pre-Qualifications [Member]
Other Intangible Assets [Line Items]
Other intangible assets, non-amortizing	72,900	72,900	72,900	74,000	77,600	$ 77,600
Other Intangible Assets [Roll Forward]
Other intangible assets, non-amortizing, beginning balance			74,000	77,600
Additions from new business combinations, non-amortizing intangible assets			200	0
Measurement period adjustments, non-amortizing intangible assets			0	0
Intangible asset impairment, non-amortizing intangible assets		(3,300)	(3,300)
Currency translation adjustments, non-amortizing intangible assets			2,000	(3,600)
Other intangible assets, non-amortizing, ending balance	$ 72,900	$ 72,900	$ 72,900	$ 74,000	$ 77,600