Goodwill and Other Intangible Assets - Summary of Changes in Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Goodwill [Roll Forward]
Goodwill gross, beginning balance	$ 1,996,362		$ 1,966,432
Accumulated impairment, beginning balance	(96,483)		(97,832)
Goodwill, beginning balance	1,899,879		1,868,600
Goodwill acquired	21,909	$ 34,300	56,337
Purchase price allocation adjustments			51
Foreign currency translation adjustments	5,240		(25,109)
Goodwill gross, ending balance	2,023,594	2,023,594	1,996,362
Accumulated impairment, ending balance	(96,566)	(96,566)	(96,483)
Goodwill, ending balance	1,927,028	1,927,028	1,899,879
Electric Power Infrastructure Services Division
Goodwill [Roll Forward]
Goodwill gross, beginning balance	1,313,078		1,272,527
Accumulated impairment, beginning balance	0		0
Goodwill, beginning balance	1,313,078		1,272,527
Goodwill acquired	21,909		56,337
Purchase price allocation adjustments			51
Foreign currency translation adjustments	3,470		(15,837)
Goodwill gross, ending balance	1,338,457	1,338,457	1,313,078
Accumulated impairment, ending balance	0	0	0
Goodwill, ending balance	1,338,457	1,338,457	1,313,078
Pipeline and Industrial Infrastructure Services Division
Goodwill [Roll Forward]
Goodwill gross, beginning balance	683,284		693,905
Accumulated impairment, beginning balance	(96,483)		(97,832)
Goodwill, beginning balance	586,801		596,073
Goodwill acquired	0		0
Purchase price allocation adjustments			0
Foreign currency translation adjustments	1,770		(9,272)
Goodwill gross, ending balance	685,137	685,137	683,284
Accumulated impairment, ending balance	(96,566)	(96,566)	(96,483)
Goodwill, ending balance	$ 588,571	$ 588,571	$ 586,801