Equity Method Investments - Equity earnings, by investment (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		$ 15,845	$ 16,237	$ 55,994	$ 60,699
White Cliffs Pipeline, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		15,555	16,047	51,763	50,682
NGL Energy Partners LP [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	[1]	(38)	(878)	2,194	5,037
Glass Mountain Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		$ 328	$ 1,068	$ 2,037	$ 4,980

[1] (1) Excluding loss on issuance of common units of $41.0 thousand for the nine months ended September 30, 2016 and a gain on the issuance of common units of $0.1 million and $6.0 million for the three and nine months ended September 30, 2015, respectively. Additionally, gains and losses on the disposal or impairment of equity investments are not reported within "earnings from equity method investments" in the condensed consolidated statements of operations and comprehensive income (loss).