Revisions in Estimates (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) project	Dec. 31, 2016 USD ($) project	Dec. 31, 2015 USD ($) project
Change in Accounting Estimate [Line Items]
Impact From Affirmative Claim Recovery Estimate	$ 34.9	$ 37.3	$ 48.5
Amount Considered Significant on Individual Project Gross Profit	1.0	1.0	1.0
Impact from estimated recovery of backcharge claims	(4.6)	(15.7)	(7.0)
Construction [Member]
Change in Accounting Estimate [Line Items]
Increase (Decrease) on Project Profitability	4.0	1.3	19.9
Contracts Accounted for under Percentage of Completion [Member] | Large Project Construction [Member]
Change in Accounting Estimate [Line Items]
Increase (Decrease) on Project Profitability	(66.6)	(13.5)	7.6
Contracts Accounted for under Percentage of Completion [Member] | Large Project Construction [Member] | Noncontrolling Interest [Member]
Change in Accounting Estimate [Line Items]
Increase (Decrease) on Project Profitability	(2.1)	(4.3)	3.0
Upward Estimate Change [Member] | Construction [Member]
Change in Accounting Estimate [Line Items]
Increase (Decrease) on Project Profitability	$ 17.2	$ 14.2	$ 30.7
Number of Projects with Estimate Changes | project	10	7	14
Upward Estimate Change [Member] | Construction [Member] | Minimum [Member]
Change in Accounting Estimate [Line Items]
Range Of Effect On Gross Profit	$ 1.1	$ 1.1	$ 1.1
Upward Estimate Change [Member] | Construction [Member] | Maximum [Member]
Change in Accounting Estimate [Line Items]
Range Of Effect On Gross Profit	3.9	4.8	6.6
Upward Estimate Change [Member] | Large Project Construction [Member]
Change in Accounting Estimate [Line Items]
Increase (Decrease) on Project Profitability	$ 2.0	$ 27.2	$ 27.9
Number of Projects with Estimate Changes | project	1	8	7
Upward Estimate Change [Member] | Large Project Construction [Member] | Minimum [Member]
Change in Accounting Estimate [Line Items]
Range Of Effect On Gross Profit	$ 2.0	$ 1.2	$ 1.5
Upward Estimate Change [Member] | Large Project Construction [Member] | Maximum [Member]
Change in Accounting Estimate [Line Items]
Range Of Effect On Gross Profit	2.0	6.5	6.7
Downward Estimate Change [Member] | Construction [Member]
Change in Accounting Estimate [Line Items]
Increase (Decrease) on Project Profitability	$ (13.2)	$ (12.9)	$ (10.8)
Number of Projects with Estimate Changes | project	6	7	5
Downward Estimate Change [Member] | Construction [Member] | Minimum [Member]
Change in Accounting Estimate [Line Items]
Range Of Effect On Gross Profit	$ (1.0)	$ (1.0)	$ (1.0)
Downward Estimate Change [Member] | Construction [Member] | Maximum [Member]
Change in Accounting Estimate [Line Items]
Range Of Effect On Gross Profit	(4.4)	(3.9)	(3.3)
Downward Estimate Change [Member] | Large Project Construction [Member]
Change in Accounting Estimate [Line Items]
Increase (Decrease) on Project Profitability	$ (68.6)	$ (40.7)	$ (20.3)
Number of Projects with Estimate Changes | project	7	5	6
Downward Estimate Change [Member] | Large Project Construction [Member] | Minimum [Member]
Change in Accounting Estimate [Line Items]
Range Of Effect On Gross Profit	$ (1.3)	$ (1.3)	$ (1.0)
Downward Estimate Change [Member] | Large Project Construction [Member] | Maximum [Member]
Change in Accounting Estimate [Line Items]
Range Of Effect On Gross Profit	(17.2)	(13.6)	(5.5)
Revisions to Estimated Total Contract Costs [Member] [Member]
Change in Accounting Estimate [Line Items]
Impact From Affirmative Claim Recovery Estimate	30.9	25.4	37.3
Impact from estimated recovery of backcharge claims	2.5	4.8	0.5
No Material Associated Cost [Member]
Change in Accounting Estimate [Line Items]
Impact From Affirmative Claim Recovery Estimate	4.0	11.9	11.2
Impact from estimated recovery of backcharge claims	$ 2.1	10.9	$ 6.5
Sales Revenue, Net [Member]
Change in Accounting Estimate [Line Items]
Quantifying Misstatement in Current Year Financial Statements, Amount		4.9
Gross Profit [Member]
Change in Accounting Estimate [Line Items]
Quantifying Misstatement in Current Year Financial Statements, Amount		$ 1.6