Members' Capital and Distributions (Details 1) (USD $)	3 Months Ended	9 Months Ended
Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2011	Sep. 30, 2010
Quarterly cash distributions
Distribution Per Unit	$ 0.575	$ 0.575	$ 0.575	$ 0.575
Date Declared	2011-10-12	2011-07-13	2011-04-13	2011-01-12
Record Date	2010-10-31	2011-08-01	2011-04-29	2011-02-01
Payment Date	2011-11-10	2011-08-11	2011-05-12	2011-02-11
Amount	$ 38,705,000	$ 38,687,000	$ 38,538,000	$ 38,456,000	$ 115,657,000	$ 108,161,000

Date of record for distribution of cash, stock, or units to a member or limited partner of LLC or LP.

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- Definition

Date of declaration for distribution of cash, stock, or units to a member or limited partner of LLC or LP.

+ Details

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- Definition

Date of distribution for distribution of cash, stock, or units to a member or limited partner of LLC or LP.

+ Details

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- Definition

Per-share or per-unit cash distributions paid to a common shareholder or unit-holder by an LLC or LP.

+ Details

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- Definition

Total distributions to each class of partners (i.e., general, limited and preferred partners).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6959260&loc=d3e187171-122770

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Emerging Issues Task Force (EITF)

-Number 87-21

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Practice Bulletin (PB)

-Number 14

-Paragraph 15

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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