Goodwill and Other Intangible Assets (Rollforward of Other Intangible Assets) (Details) - USD ($) $ in Thousands			12 Months Ended
		Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Intangible Assets [Line Items]
Other intangible assets, gross carrying amount					$ 329,300
Accumulated amortization					(129,900)
Other Intangible Assets [Roll Forward]
Other intangible assets, net, beginning balance			$ 179,711	$ 199,400
Amortization expense			(20,900)	(21,300)	(28,400)
Currency translation adjustments			3,500	1,600
Other activity, intangible assets				0
Additions from new business combinations, intangible assets			28,800
Other intangible assets, net, amortizing, ending balance		$ 79,000	79,000
Other intangible assets, net, ending balance		$ 191,142	191,142	179,711	199,400
Weighted Average [Member]
Other Intangible Assets [Line Items]
Remaining weighted average amortization period (in years)		9 years
Customer Relationships and Backlog [Member]
Other Intangible Assets [Line Items]
Other intangible assets, amortizing, gross carrying amount					195,400
Accumulated amortization					(114,600)
Other Intangible Assets [Roll Forward]
Other intangible assets, net, amortizing, beginning balance			63,200	80,800
Amortization expense			(19,300)	(17,900)
Currency translation adjustments, amortizing intangible assets			400	300
Other activity, intangible assets				0
Additions from new business combinations, amortizing intangible assets			26,300
Other intangible assets, net, amortizing, ending balance		$ 70,600	70,600	63,200	80,800
Customer Relationships and Backlog [Member] | Weighted Average [Member]
Other Intangible Assets [Line Items]
Remaining weighted average amortization period (in years)		9 years
Other Amortizing Intangible Assets [Member]
Other Intangible Assets [Line Items]
Other intangible assets, amortizing, gross carrying amount	[1]				25,700
Accumulated amortization	[1]				(15,300)
Other Intangible Assets [Roll Forward]
Other intangible assets, net, amortizing, beginning balance	[1]		7,400	10,400
Amortization expense	[1]		(1,600)	(3,400)
Currency translation adjustments, amortizing intangible assets	[1]		100	100
Other activity, intangible assets	[1]			300
Additions from new business combinations, amortizing intangible assets			2,500
Other intangible assets, net, amortizing, ending balance	[1]	$ 8,400	8,400	7,400	10,400
Other Amortizing Intangible Assets [Member] | Weighted Average [Member]
Other Intangible Assets [Line Items]
Remaining weighted average amortization period (in years)	[1]	8 years
Trade Names [Member]
Other Intangible Assets [Line Items]
Other intangible assets, non-amortizing, beginning balance			34,500	34,800
Other Intangible Assets [Roll Forward]
Other intangible assets, non-amortizing, beginning balance			34,500	34,800
Currency translation adjustments, non-amortizing intangible assets			0	0
Other activity, intangible assets				(300)
Additions from new business combinations, non-amortizing intangible assets			0
Other intangible assets, non-amortizing, ending balance		$ 34,500	34,500	34,500	34,800
Pre-Qualifications [Member]
Other Intangible Assets [Line Items]
Other intangible assets, non-amortizing, beginning balance			74,600	73,400
Other Intangible Assets [Roll Forward]
Other intangible assets, non-amortizing, beginning balance			74,600	73,400
Currency translation adjustments, non-amortizing intangible assets			3,000	1,200
Other activity, intangible assets				0
Additions from new business combinations, non-amortizing intangible assets			0
Other intangible assets, non-amortizing, ending balance		$ 77,600	$ 77,600	$ 74,600	$ 73,400

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