The Company (Details)	12 Months Ended
Dec. 31, 2012
Common partnership interests of DRLP owned	98.40%
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest	1.60%

The number of units or percentage investment held by the managing member or general partner of the LLC or LP.

Reference 1: 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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 272

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration