Operating Information by Segment and Geographic Area - Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
TOTAL REVENUE	$ 3,937,707	$ 3,842,235	$ 10,622,201	$ 11,268,305
Energy & Chemicals
Segment Reporting Information [Line Items]
TOTAL REVENUE	1,611,600	1,902,300	4,485,200	5,859,800
Mining & Industrial
Segment Reporting Information [Line Items]
TOTAL REVENUE	1,374,000	973,300	3,703,600	2,377,400
Infrastructure & Power
Segment Reporting Information [Line Items]
TOTAL REVENUE	392,500	412,300	951,800	1,250,600
Diversified Services
Segment Reporting Information [Line Items]
TOTAL REVENUE	521,700	526,300	1,525,000	1,706,900
Other
Segment Reporting Information [Line Items]
TOTAL REVENUE	37,900	28,000	(43,400)	73,600
Intercompany | Diversified Services
Segment Reporting Information [Line Items]
TOTAL REVENUE	$ 81,000	$ 73,000	$ 253,000	$ 257,000