Operating Information by Segment and Geographic Area - Total Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Segment reporting information
Total assets	$ 7,883,707	$ 8,913,637
Other
Segment reporting information
Total assets	46,300	104,600
Corporate
Segment reporting information
Total assets	3,361,000	3,513,900
Reportable segments | Energy & Chemicals
Segment reporting information
Total assets	1,170,500	1,525,100
Reportable segments | Mining & Industrial
Segment reporting information
Total assets	547,500	694,800
Reportable segments | Infrastructure & Power
Segment reporting information
Total assets	439,000	498,400
Reportable segments | Diversified Services
Segment reporting information
Total assets	$ 1,322,200	$ 1,414,600