Certain provisions of the partnership agreement 1 (Details) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Common Stock [Member]
Distribution Made to Member or Limited Partner [Line Items]
Distributed earning allocated to:	$ 5,687	$ 4,719	$ 16,578	$ 12,720
Undistributed loss allocated to:	(9,885)	(6,275)	(23,207)	(16,821)
Net Loss allocated to:	(4,198)	(1,556)	(6,629)	(4,101)
Restricted Stock Units (RSUs) [Member]
Distribution Made to Member or Limited Partner [Line Items]
Distributed earning allocated to:	170	115	500	305
Undistributed loss allocated to:	(286)	(147)	(681)	(402)
Net Loss allocated to:	(116)	(32)	(181)	(97)
Total [Member]
Distribution Made to Member or Limited Partner [Line Items]
Distributed earning allocated to:	5,857	4,834	17,078	13,025
Undistributed loss allocated to:	(10,171)	(6,422)	(23,888)	(17,223)
Net Loss allocated to:	$ (4,314)	$ (1,588)	$ (6,810)	$ (4,198)
Basic and diluted common units	$ (0.09)	$ (0.04)	$ (0.14)	$ (0.09)