Revenue - Construction Segment Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue	$ 394.8	$ 170.5	$ 810.4	$ 538.9
Total revenue	394.8	170.5	810.4	538.9
Infrastructure
Disaggregation of Revenue [Line Items]
Revenue	383.0	160.7	776.3	508.9
Other revenue	0.0	0.1	0.0	0.7
Total revenue	383.0	160.8	776.3	509.6
Infrastructure | Commercial
Disaggregation of Revenue [Line Items]
Revenue	207.0	48.2	343.3	165.0
Infrastructure | Industrial
Disaggregation of Revenue [Line Items]
Revenue	92.9	52.2	207.9	170.6
Infrastructure | Transportation
Disaggregation of Revenue [Line Items]
Revenue	16.0	18.2	40.0	58.0
Infrastructure | Government
Disaggregation of Revenue [Line Items]
Revenue	15.9	17.5	54.6	37.2
Infrastructure | Leisure
Disaggregation of Revenue [Line Items]
Revenue	4.8	8.2	16.5	35.5
Infrastructure | Healthcare
Disaggregation of Revenue [Line Items]
Revenue	17.1	7.9	37.2	20.6
Infrastructure | Convention
Disaggregation of Revenue [Line Items]
Revenue	23.4	1.2	51.7	5.0
Infrastructure | Other
Disaggregation of Revenue [Line Items]
Revenue	$ 5.9	$ 7.3	$ 25.1	$ 17.0