Revisions in Estimates - Additional Information(Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2018
Change In Accounting Estimate [Line Items]
Impact from affirmative claim recovery estimate	$ 2.3	$ 12.2	$ 4.9	$ 14.0
Impact from estimated recovery of back charge claims	(1.6)	2.7	(2.0)	3.0
Minimum [Member] | Subsequent Event [Member]
Change In Accounting Estimate [Line Items]
Decrease on project revenue and profitability					$ 0.0
Maximum [Member] | Subsequent Event [Member]
Change In Accounting Estimate [Line Items]
Decrease on project revenue and profitability					$ 15.0
Revisions to Estimated Total Contract Costs [Member]
Change In Accounting Estimate [Line Items]
Impact from affirmative claim recovery estimate	6.4		8.5
Impact from estimated recovery of back charge claims	0.9	1.4	1.1	1.4
Estimated Costs Recorded in Prior Period [Member]
Change In Accounting Estimate [Line Items]
Impact from affirmative claim recovery estimate	(4.1)	0.8	(3.6)	(0.1)
Impact from estimated recovery of back charge claims	0.7	1.3	0.9	1.6
Revisions to Estimated Total Contract Costs [Member]
Change In Accounting Estimate [Line Items]
Impact from affirmative claim recovery estimate		11.4		14.1
Large Project Construction [Member]
Change In Accounting Estimate [Line Items]
Decrease on project revenue and profitability			4.9
Increase in net loss			1.6
Change in accounting estimate amount considered significant to individual project gross profit			1.0
Large Project Construction [Member] | Net Estimate Change [Member]
Change In Accounting Estimate [Line Items]
Increase (decrease) on project profitability	(30.3)	(23.8)	(39.8)	(37.8)
Large Project Construction [Member] | Contracts Accounted for under Percentage of Completion [Member] | Noncontrolling Interest [Member]
Change In Accounting Estimate [Line Items]
Increase (decrease) on project profitability	0.0	(0.4)	0.0	(2.0)
Construction Segment [Member]
Change In Accounting Estimate [Line Items]
Change in accounting estimate amount considered significant to individual project gross profit			1.0
Construction Segment [Member] | Net Estimate Change [Member]
Change In Accounting Estimate [Line Items]
Increase (decrease) on project profitability	$ (4.5)	$ (1.1)	$ (3.3)	$ (1.8)