Operating Information by Segment and Geographic Area - Total Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Assets	$ 7,258,083	$ 7,309,812
Reportable segments | Energy Solutions
Segment Reporting Information [Line Items]
Assets	1,196,200	1,010,900
Reportable segments | Urban Solutions
Segment Reporting Information [Line Items]
Assets	1,110,400	1,122,500
Reportable segments | Mission Solutions
Segment Reporting Information [Line Items]
Assets	629,000	575,800
Reportable segments | Other
Segment Reporting Information [Line Items]
Assets	$ 38,500	$ 37,800