Transactions with Affiliates Related Party Transations (Details) $ in Thousands	1 Months Ended	3 Months Ended
	Apr. 30, 2019 USD ($)	Mar. 31, 2019 USD ($) employee	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Related Party Transaction [Line Items]
Advances from affiliates		$ 86,580		$ 0
Advances to affiliate		$ 0		$ 33,034
Related party transaction, rate		2.33%
Entity number of employees | employee		0
Expenses, related party		$ 92,200	$ 91,500
Equity distributions to parent		176,000	55,000
Cash contributions from parent		0	340,000
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Operating revenues, related party		3,300	1,800
Cost of natural gas sales, related party		1,600	1,900
Expenses, related party		$ (1,200)	$ (1,000)
Subsequent Event [Member]
Related Party Transaction [Line Items]
Equity distributions to parent	$ 170,000