Components of Working Capital - Other Current Assets Table (Details) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
Other Current Assets [Line Items]
Natural gas liquids inventory		$ 11,212	$ 10,788
Imbalance receivables		3,829	1,640
Prepaid insurance		3,203	2,955
Contract assets		2,748	0
Other		5,127	0
Total other current assets	[1]	$ 26,119	$ 15,383

[1] Other current assets includes affiliate amounts of $1.4 million and zero as of September 30, 2018, and December 31, 2017, respectively.