Goodwill and Other Intangible Assets (Rollforward of Other Intangible Assets) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Other Intangible Assets [Line Items]
Other intangible assets, gross				$ 354,000
Accumulated amortization				(184,600)
Other Intangible Assets [Rollforward]
Other intangible assets, net, beginning balance		$ 169,370
Additions from new business combinations		27,600
Amortization expense		(4,800)	$ (4,900)
Currency translation adjustments		1,000
Other intangible assets, net, ending balance		193,192
Customer Relationships and Backlog [Member]
Other Intangible Assets [Line Items]
Other intangible assets, amortizing, gross				224,400
Accumulated amortization				(170,000)
Other Intangible Assets [Rollforward]
Other intangible assets, net, amortizing, beginning balance		54,400
Additions from new business combinations, amortizing intangible assets		26,000
Amortization expense		(4,400)
Currency translation adjustments, amortizing intangible assets		100
Other intangible assets, net, amortizing, ending balance		76,100
Other Amortizing Intangible Assets [Member]
Other Intangible Assets [Line Items]
Other intangible assets, amortizing, gross	[1]			21,100
Accumulated amortization	[1]			(14,600)
Other Intangible Assets [Rollforward]
Other intangible assets, net, amortizing, beginning balance	[1]	6,500
Additions from new business combinations, amortizing intangible assets	[1]	1,600
Amortization expense	[1]	(400)
Currency translation adjustments, amortizing intangible assets	[1]	0
Other intangible assets, net, amortizing, ending balance	[1]	7,700
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
Pre-Qualifications [Member]
Other Intangible Assets [Line Items]
Other intangible assets, non-amortizing		74,000		$ 74,000
Other Intangible Assets [Rollforward]
Other intangible assets, non-amortizing, beginning balance		74,000
Additions from new business combinations, non-amortizing intangible assets		0
Currency translation adjustments, non-amortizing intangible assets		900
Other intangible assets, non-amortizing, ending balance		$ 74,900

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