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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 142
-Paragraph 45
-Subparagraph a(1)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6905858&loc=d3e16323-109275

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The maximum useful life of a major finite-lived intangible asset class. A major class is composed of intangible assets that can be grouped together because they are similar either by their nature or by their use in the operations of a company.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 35
-Paragraph 3
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-URI http://asc.fasb.org/extlink&oid=6904245&loc=d3e15211-109273

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The minimum useful life of a major finite-lived intangible asset class. A major class is composed of intangible assets that can be grouped together because they are similar either by their nature or by their use in the operations of a company.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Significant Accounting Policies (Details) (USD $)	3 Months Ended		6 Months Ended
Significant Accounting Policies (Details) (USD $)	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Investment in Commercial Real Estate Properties
Estimated useful life of other intangible assets, low end of range			1
Estimated useful life of other intangible assets, high end of range			14
Increase in rental revenue from amortization of acquired leases	$ 5,000,000	$ 6,200,000	$ 12,200,000	$ 12,800,000
Reduction in interest expense from amortization of above-market rate mortgages	1,800,000	600,000	3,200,000	900,000
Identified intangible assets (included in other assets):
Gross amount	567,046,000		567,046,000		758,300,000
Accumulated amortization	(157,411,000)		(157,411,000)		(133,737,000)
Net	409,635,000		409,635,000		624,563,000
Identified intangible liabilities (included in deferred revenue):
Gross amount	534,227,000		534,227,000		508,339,000
Accumulated amortization	(252,753,000)		(252,753,000)		(220,417,000)
Net	$ 281,474,000		$ 281,474,000		$ 287,922,000
Buildings
Investment in Commercial Real Estate Properties
Estimated useful life, low end of range			3
Estimated useful life, high end of range			40
Above-market leases
Investment in Commercial Real Estate Properties
Estimated useful life of other intangible assets, low end of range			1
Estimated useful life of other intangible assets, high end of range			14
Below-market leases
Investment in Commercial Real Estate Properties
Estimated useful life of other intangible assets, low end of range			1
Estimated useful life of other intangible assets, high end of range			14
In-place leases
Investment in Commercial Real Estate Properties
Estimated useful life of other intangible assets, low end of range			1
Estimated useful life of other intangible assets, high end of range			14