Certain provisions of the partnership agreement (Details 1) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Common Stock [Member]
Distribution Made to Member or Limited Partner [Line Items]
Distributed earning allocated to:	$ 5,682	$ 4,239	$ 10,891	$ 8,002
Undistributed loss allocated to:	(7,307)	(5,281)	(13,323)	(10,546)
Net Loss allocated to:	(1,625)	(1,042)	(2,432)	(2,544)
Restricted Stock Units (RSUs) [Member]
Distribution Made to Member or Limited Partner [Line Items]
Distributed earning allocated to:	172	115	330	190
Undistributed loss allocated to:	(219)	(146)	(394)	(255)
Net Loss allocated to:	(47)	(31)	(64)	(65)
Total [Member]
Distribution Made to Member or Limited Partner [Line Items]
Distributed earning allocated to:	5,854	4,354	11,221	8,192
Undistributed loss allocated to:	(7,526)	(5,427)	(13,717)	(10,801)
Net Loss allocated to:	$ (1,672)	$ (1,073)	$ (2,496)	$ (2,609)
Basic and diluted common units	$ (0.03)	$ (0.02)	$ (0.05)	$ (0.05)