Contract Assets and Liabilities - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) project	Dec. 31, 2019 USD ($) project
Property, Plant and Equipment [Line Items]
Percentage completed of certain milestones	10.00%
Net amount of unresolved change orders and claims	$ 33.6	$ 38.4
Revision in contract estimates, project write down	$ 10.4	$ 12.4
Number of projects | project	15	16
Southern California Region Project
Property, Plant and Equipment [Line Items]
Revision in contract estimates, project write down	$ 6.9	$ 9.9
Number of projects | project	8	12
Mid-Atlantic Region Project
Property, Plant and Equipment [Line Items]
Revision in contract estimates, project write down	$ 1.5
Number of projects | project	3
New England Region Project
Property, Plant and Equipment [Line Items]
Revision in contract estimates, project write down	$ 1.1
Number of projects | project	2
Various Other Region Projects
Property, Plant and Equipment [Line Items]
Revision in contract estimates, project write down	$ 0.9
Number of projects | project	2
Construction Projects
Property, Plant and Equipment [Line Items]
Number of projects | project	3	10
Revision in contract estimates, gross profit write up	$ 1.7	$ 4.7
Ohio Region Project
Property, Plant and Equipment [Line Items]
Number of projects | project	2
Revision in contract estimates, gross profit write up	$ 1.3
Single Mid-Atlantic Region Project
Property, Plant and Equipment [Line Items]
Number of projects | project	1	1
Revision in contract estimates, gross profit write up	$ 0.3	$ 0.3
Western Pennsylvania Region Project
Property, Plant and Equipment [Line Items]
Revision in contract estimates, project write down		$ 1.4
Number of projects | project		1
Southern California Region Service Project
Property, Plant and Equipment [Line Items]
Number of projects | project		1
Revision in contract estimates, gross profit write down		$ 0.4
Single Southern California Region Project
Property, Plant and Equipment [Line Items]
Number of projects | project		1
Revision in contract estimates, gross profit write up		$ 0.4