Equity Method Investments - Equity earnings, by investment (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		$ 17,078	$ 23,903	$ 40,149	$ 44,462
White Cliffs Pipeline, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		16,428	15,545	36,208	34,635
NGL Energy Partners LP [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments	[1]	0	6,220	2,232	5,915
Glass Mountain Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		$ 650	$ 2,138	$ 1,709	$ 3,912

[1] (1) Excluding loss on issuance of common units of $41.0 thousand for the six months ended June 30, 2016 and a gain on the issuance of common units of $5.9 million for the three and six months ended June 30, 2015. 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).