Equity Method Investments - Investment balances (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 446,938	$ 551,078
White Cliffs Pipeline, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	290,668	297,109
NGL Energy Partners LP [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	18,977	112,787
Glass Mountain Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 137,293	$ 141,182