CONSOLIDATED STATEMENTS OF MEMBERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Member Units	Cumulative Preferred units Member Units	Common Units Member Units	Class B Units Member Units
Balance at Dec. 31, 2013		$ 1,268,335	$ 61,021	$ 1,199,699	$ 7,615
Increase (Decrease) in Members' Equity [Roll Forward]
Issuance of units, net of offering costs			274,423	147,814
Repurchase of units under the common unit buyback program		(2,498)		(2,498)
Distributions to Preferred unitholders		(18,197)		(18,197)
Distributions to Common and Class B unitholders		(207,883)		(207,883)
Unit-based compensation		7,777		7,777
Net income		64,345		64,345
Balance at Dec. 31, 2014		1,534,116	335,444	1,191,057	7,615
Increase (Decrease) in Members' Equity [Roll Forward]
Issuance of units, net of offering costs		32,737		32,737
Repurchase of units under the common unit buyback program		(2,399)		(2,399)
Distributions to Preferred unitholders		(13,380)		(13,380)
Distributions to Common and Class B unitholders		(68,380)		(68,380)
Unit-based compensation		7,420		7,420
Net income	$ (912,475)	(912,475)		(912,475)
Balance at Jun. 30, 2015		$ 577,639	$ 335,444	$ 234,580	$ 7,615