Revenue - Construction Segment Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue	$ 243.8	$ 181.8	$ 415.6	$ 368.4
Total revenue	243.8	181.8	415.6	368.4
Infrastructure
Disaggregation of Revenue [Line Items]
Revenue	232.0	171.7	393.3	348.2
Other revenue	0.0	0.6	0.0	0.6
Total revenue	232.0	172.3	393.3	348.8
Infrastructure | Commercial
Disaggregation of Revenue [Line Items]
Revenue	84.8	54.0	134.3	116.8
Infrastructure | Industrial
Disaggregation of Revenue [Line Items]
Revenue	79.0	59.6	119.2	118.4
Infrastructure | Transportation
Disaggregation of Revenue [Line Items]
Revenue	10.8	23.5	24.7	39.9
Infrastructure | Government
Disaggregation of Revenue [Line Items]
Revenue	17.2	11.1	38.5	19.7
Infrastructure | Leisure
Disaggregation of Revenue [Line Items]
Revenue	4.7	11.3	12.2	27.3
Infrastructure | Healthcare
Disaggregation of Revenue [Line Items]
Revenue	11.1	4.7	20.0	12.6
Infrastructure | Convention
Disaggregation of Revenue [Line Items]
Revenue	18.8	1.4	28.2	3.8
Infrastructure | Other
Disaggregation of Revenue [Line Items]
Revenue	$ 5.6	$ 6.1	$ 16.2	$ 9.7