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

Aggregate dividends paid during the period for each share of common stock outstanding.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=6959260&loc=d3e187085-122770

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