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Nature of Business (Details) $ in Thousands								12 Months Ended
	Jul. 01, 2018 USD ($)	Jun. 01, 2018 USD ($) segment	Jun. 16, 2017 USD ($)	May 30, 2017 USD ($)	May 26, 2017 USD ($)	Nov. 18, 2016 USD ($)	Jan. 29, 2016 USD ($)	Dec. 31, 2018 USD ($) segment item	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Nature of Business
Number of reportable segments | segment								5
Number of joint ventures | item								2
Number of variable interest entities | item								2
Purchase consideration, net of cash acquired								$ 110,620	$ 66,205	$ 10,997
Capitalized property, plant and equipment								$ 732,720	$ 614,889
Northern
Nature of Business
Total purchase consideration						$ 6,900
Mueller
Nature of Business
Total purchase consideration							$ 4,100
Willbros Group, Inc
Nature of Business
Number of reportable segments | segment		2
Purchase consideration, net of cash acquired	$ 110,600	$ 110,620
Total purchase consideration		164,758
Transmission | Willbros Group, Inc
Nature of Business
Purchase consideration, net of cash acquired		$ 110,600
Utilities | Mueller
Nature of Business
Total purchase consideration							$ 4,100
Utilities | FGC
Nature of Business
Total purchase consideration					$ 37,700
Pipeline | Coastal
Nature of Business
Total purchase consideration			$ 27,500
Power
Nature of Business
Number of joint ventures | item								2
Power | Northern
Nature of Business
Total purchase consideration						$ 6,900
Power | Engineering Assets
Nature of Business
Total purchase consideration				$ 2,300
Carlsbad
Nature of Business
Ownership percentage								50.00%
Wilmington
Nature of Business
Ownership percentage								50.00%

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