Goodwill and Other Intangible Assets (Rollforward of Other Intangible Assets) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Other Intangible Assets [Line Items]
Other intangible assets, gross						$ 323,300
Accumulated amortization						(143,600)
Other Intangible Assets [Rollforward]
Other intangible assets, net, beginning balance				$ 179,711
Additions from new business combinations, other intangible assets				26,800
Amortization expense		$ (6,000)	$ (5,200)	(15,000)	$ (15,700)
Currency translation adjustments, other intangible assets				4,000
Other intangible assets, net, ending balance		195,454		195,454
Customer Relationships and Backlog [Member]
Other Intangible Assets [Line Items]
Other intangible assets, amortizing, gross						195,100
Accumulated amortization						(131,900)
Other Intangible Assets [Rollforward]
Other intangible assets, net, amortizing, beginning balance				63,200
Additions from new business combinations, amortizing intangible assets				24,400
Amortization expense				(13,900)
Currency translation adjustments, amortizing intangible assets				500
Other intangible assets, net, amortizing, ending balance		74,200		74,200
Other Amortizing Intangible Assets [Member]
Other Intangible Assets [Line Items]
Other intangible assets, amortizing, gross	[1]					19,100
Accumulated amortization	[1]					(11,700)
Other Intangible Assets [Rollforward]
Other intangible assets, net, amortizing, beginning balance	[1]			7,400
Additions from new business combinations, amortizing intangible assets				2,400
Amortization expense	[1]			(1,100)
Currency translation adjustments, amortizing intangible assets	[1]			100
Other intangible assets, net, amortizing, ending balance	[1]	8,800		8,800
Trade Names [Member]
Other Intangible Assets [Line Items]
Other intangible assets, non-amortizing, carrying amount		34,500		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		34,500
Pre-Qualifications [Member]
Other Intangible Assets [Line Items]
Other intangible assets, non-amortizing, carrying amount		78,000		74,600		$ 74,600
Other Intangible Assets [Rollforward]
Other intangible assets, non-amortizing, beginning balance				74,600
Additions from new business combinations, non-amortizing intangible assets				0
Currency translation adjustments, non-amortizing intangible assets				3,400
Other intangible assets, non-amortizing, ending balance		$ 78,000		$ 78,000

[1] Consists principally of trade names and non-compete agreements.