Goodwill and Other Intangible Assets (Rollforward of Other Intangible Assets) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 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				28,600
Measurement period adjustments	[1]			(300)
Amortization expense		$ (4,700)	$ (5,400)	(9,500)	$ (10,300)
Currency translation adjustments				1,900
Other intangible assets, net, ending balance		190,149		190,149
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				27,000
Measurement period adjustments, amortizing intangible assets	[1]			(300)
Amortization expense				(8,600)
Currency translation adjustments, amortizing intangible assets				100
Other intangible assets, net, amortizing, ending balance		72,600		72,600
Other Amortizing Intangible Assets [Member]
Other Intangible Assets [Line Items]
Other intangible assets, amortizing, gross	[2]					21,100
Accumulated amortization	[2]					(14,600)
Other Intangible Assets [Rollforward]
Other intangible assets, net, amortizing, beginning balance	[2]			6,500
Additions from new business combinations, amortizing intangible assets	[2]			1,600
Measurement period adjustments, amortizing intangible assets	[1],[2]			0
Amortization expense	[2]			(900)
Currency translation adjustments, amortizing intangible assets	[2]			0
Other intangible assets, net, amortizing, ending balance	[2]	7,200		7,200
Trade Names [Member]
Other Intangible Assets [Line Items]
Other intangible assets, non-amortizing		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
Measurement period adjustments, non-amortizing intangible assets	[1]			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		75,800		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
Measurement period adjustments, non-amortizing intangible assets	[1]			0
Currency translation adjustments, non-amortizing intangible assets				1,800
Other intangible assets, non-amortizing, ending balance		$ 75,800		$ 75,800

[1] Represents adjustments to preliminary estimates of fair value within the measurement period of up to one year from the date of acquisition.

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