Real Estate Investments (Details 2) (Three Logan Square [Member], USD $) In Thousands, unless otherwise specified	6 Months Ended
Jun. 30, 2011	Aug. 05, 2010
Intangible assets
Intangible assets acquired		$ 28,856
Weighted Average Amortization Period (in years)	23
Intangible liabilities:
Below market leases assumed		683
Weighted Average Amortization Period (in years)	1
Leases, Acquired-in-Place [Member]
Intangible assets
Intangible assets acquired		13,584
Weighted Average Amortization Period (in years)	3
Customer Relationships [Member]
Intangible assets
Intangible assets acquired		8,870
Weighted Average Amortization Period (in years)	5
Above market tenant leases acquired [Member]
Intangible assets
Intangible assets acquired		895
Weighted Average Amortization Period (in years)	1
Below market ground lease acquired [Member]
Intangible assets
Intangible assets acquired		5,507
Weighted Average Amortization Period (in years)	82
Intangible liabilities:
Below market leases assumed		$ 683

Intangible liabilities.

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Weighted Average Amortization Period Intangible liabilities.

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The aggregate amount assigned to a major class of finite-lived intangible assets acquired either individually or as part of a group of assets (in either an asset acquisition or business combination). 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 142
-Paragraph 44
-Subparagraph a(1)

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The calculated weighted-average amortization period of a major class of finite-lived intangible assets acquired during the current period either individually or as part of a group of assets (in either an asset acquisition or business combination). 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 142
-Paragraph 44
-Subparagraph a(3)

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- Definition

The amount of acquisition cost of a business combination allocated to liabilities assumed.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141
-Paragraph 37
-Subparagraph g

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Emerging Issues Task Force (EITF)
-Number 98-1

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