Investments in Non-Consolidated Subsidiaries - Equity earnings, by investment (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	$ 14,962		$ 17,345
White Cliffs Pipeline, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	11,080		10,439
NGL Energy Partners LP [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	3,591	[1]	6,916
Glass Mountain Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	$ 291		$ (10)

[1] * Excluding gain on issuance of common units of $8.1 million.