Investments in Non-Consolidated Subsidiaries - Equity method investments (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 633,375	$ 565,124
White Cliffs Pipeline, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	271,187	224,095
NGL Energy Partners LP [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	214,522	208,848
Glass Mountain Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 147,666	$ 132,181