Nature of Business (Details) $ in Millions						6 Months Ended	12 Months Ended
	Jun. 16, 2017 USD ($)	May 30, 2017 USD ($)	May 26, 2017 USD ($)	Nov. 18, 2016 USD ($)	Jan. 29, 2016 USD ($)	Jun. 30, 2017 segment item	Dec. 31, 2016 segment
Nature of Business
Number of reportable segments | segment						4	3
Number of joint ventures | item						2
Number of variable interest entities | item						2
Amount of purchase of assets and liabilities		$ 2.3
Pipeline | Northern
Nature of Business
Amount of purchase of assets and liabilities				$ 6.8
Pipeline | Coastal
Nature of Business
Amount of purchase of assets and liabilities	$ 27.5
Utilities | Mueller
Nature of Business
Amount of purchase of assets and liabilities					$ 4.1
Utilities | FGC
Nature of Business
Amount of purchase of assets and liabilities			$ 37.7
Carlsbad
Nature of Business
Ownership percentage						50.00%
Wilmington
Nature of Business
Ownership percentage						50.00%