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Investment in Unconsolidated Ventures (Details Textuals 1) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended |  |  |
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Mar. 31, 2011 | Sep. 30, 2011 Property Tenants Year sqft ac Room Buildings | Dec. 31, 2012 | Jun. 29, 2011 sqft | Nov. 30, 2010 PartnershipUnit Buildings
Investment in Unconsolidated Ventures (Textuals) [Abstract] |  |  |  |  |
Number of unconsolidated Real Estate Ventures |  | 16 |  |  |
Number of office buildings owned by 14 Real Estate Ventures |  | 49 |  |  |
Number of real estate ventures that owns 49 office buildings |  | 14 |  |  |
Net rentable square feet of 49 office buildings owned the 14 Real Estate Ventures |  | 6,100,000 |  |  |
Number of rooms in a hotel property developed by one Real Estate Venture |  | 137 |  |  |
Minimum ownership interest in unconsolidated Real Estate Ventures |  | 20.00% |  |  |
Maximum ownership interest in unconsolidated Real Estate Ventures |  | 65.00% |  |  |
Percentage of interest acquired in partnerships |  |  |  |  | 25.00%
Interest acquired in partnerships, Number |  |  |  |  | 2
Number of office buildings owned |  |  |  |  | 2
Percentage of interest acquired in partnerships by other partner |  |  |  |  | 75.00%
Initial contribution for acquisition of partnerships |  |  |  |  | $ 5.0
Contribution for acquisition of partnerships |  |  |  |  | 25.0
Remaining portion of contribution |  |  | 20.0 |  |
Company's ownership percentage in the Real Estate Venture |  |  |  | 3.00% |
Net rentable square feet of properties sold |  |  |  | 347,620 |
Sales price of properties sold |  |  |  | 86.7 |
Gain on sale of ownership interest | $ 2.8 |  |  |  |
Property occupied as of date of sale |  |  |  | 87.00% |

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- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 159 -Paragraph 18 -Subparagraph f -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 AICPA -Name Accounting Principles Board Opinion (APB) -Number 18 -Paragraph 20 -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 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571 + Details
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