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Risk Management and Use of Financial Instruments (Details) (USD $) In Millions, unless otherwise specified | 1 Months Ended | 3 Months Ended | 6 Months Ended
--- | --- | --- | ---
Mar. 31, 2011 | Jun. 30, 2011 | Mar. 31, 2011 | Jun. 30, 2010 | Jun. 30, 2011 | Jun. 30, 2010
Risk Management and use of Financial Instruments (Textuals) [Abstract] |  |  |  |  |  |
Anticipation of the offering of unsecured guaranteed notes due | $ 325.0 |  | $ 325.0 |  |  |
Interest rates of unsecured guaranteed notes due | 4.95% |  | 4.95% |  |  |
Treasury lock agreements |  |  |  |  | seven intra-day treasury lock agreements |
Total notional amount of the treasury lock agreements |  | 230.0 |  |  | 230.0 |
Expiration period of treasury lock agreements |  |  |  |  | 7 years |
Treasury rates, Minimum |  |  | 2.858% |  |  |
Treasury rates, Average |  |  | 2.873% |  |  |
Treasury rates, Maximum |  |  | 2.891% |  |  |
Fair Value Treasury Lock Agreements | 0.6 |  |  |  |  |
Total expense of debt offering |  | $ 0.6 |  |  | $ 0.6 |
No. of tenants accounted for 10% or more of the Company's rents |  | 0 |  | 0 | 0 | 0

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- Definition Derivative treasury lock agreements. + Details
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- Definition Expense of debt offering. + Details
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- Definition Fair value treasury lock agreements. + Details
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- Definition Treasury rates average. + Details
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- Definition Treasury rates maximum. + Details
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- Definition Treasury rates minimum. + Details
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- Definition Total monetary amount specified by the derivative(s). Expressed as an absolute value. + Details
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- Definition Interest rate stated in the contractual debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 + Details
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- Definition Amount of the hedged item as of the balance sheet date related to the derivative. For example, the hedged balance on a debt instrument. + Details
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