Statements of Changes In Members' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Units	Management Units	Class A preferred units Preferred Units	Class B preferred units Preferred Units	Class C preferred units Preferred Units
Balance at Dec. 31, 2012	$ 429,782	$ 65,043	$ 14,228	$ 205,970	$ 21,681	$ 122,860
Balance (in units) at Dec. 31, 2012		4,500	3,194	14,250	1,500	8,500
Increase (Decrease) in Members' Equity
Stock-compensation expense	473	67	47	211	22	126
Distribution to members	(10,000)	(1,565)		(4,956)	(522)	(2,957)
Net income	47,411	6,679	4,739	21,151	2,227	12,615
Balance at Jun. 30, 2013	$ 467,666	$ 70,224	$ 19,014	$ 222,376	$ 23,408	$ 132,644
Balance (in units) at Jun. 30, 2013		4,500	3,194	14,250	1,500	8,500