Operating Information by Segment and Geographic Area - Total Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Assets	$ 7,240,774	$ 7,966,658
Other
Segment Reporting Information [Line Items]
Assets	37,200	68,500
Corporate
Segment Reporting Information [Line Items]
Assets	3,345,800	3,379,300
Reportable segments | Energy & Chemicals
Segment Reporting Information [Line Items]
Assets	961,500	1,139,300
Reportable segments | Mining & Industrial
Segment Reporting Information [Line Items]
Assets	549,600	594,900
Reportable segments | Infrastructure
Segment Reporting Information [Line Items]
Assets	540,600	471,200
Reportable segments | Government
Segment Reporting Information [Line Items]
Assets	594,600	629,100
Reportable segments | Diversified Services
Segment Reporting Information [Line Items]
Assets	$ 951,800	$ 1,290,600