Certain provisions of the partnership agreement (Details Textuals 2) (Cash Distribution [Member], USD $)	3 Months Ended	6 Months Ended
	Mar. 31, 2012	Jun. 30, 2012
Cash Distribution [Member]
Distribution Made To Common And Preferred Units Holders [Line Items]
Distribution Made to Member or Limited Partner, Distribution Date	May 15, 2012	August 14, 2012
Common Stock, Dividends, Per Share, Cash Paid	$ 0.33	$ 0.33
Preferred Stock, Dividends, Per Share, Cash Paid	$ 0.33	$ 0.33