Fair Value of Financial Assets and Liabilities (Details) (USD $) In Millions	9 Months Ended	12 Months Ended
Sep. 30, 2011	Dec. 31, 2010
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Financial Assets [Abstract]
Notes receivable issued in connection with Crest property sales	$ 22.0	$ 22.1
Financial Liabilities [Abstract]
Mortgages payable	68.2
Notes payable	1,750.0	1,600.0
Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Assets [Abstract]
Notes receivable issued in connection with Crest property sales	23.0	23.2
Fair value estimate methodology for notes receivable issued in connection with Crest property sales	Discounting future cash flows using an interest rate based upon the current 5-year or 7-year Treasury yield curve, plus an applicable credit-adjusted spread	Discounting future cash flows using an interest rate based upon the current 5-year or 7-year Treasury yield curve, plus an applicable credit-adjusted spread
Financial Liabilities [Abstract]
Mortgages payable	68.1
Notes payable	$ 1,874.4	$ 1,707.1
Fair value estimate methodology for our mortgages payable	Discounting future cash flows using an interest rate based upon the current 5-year Treasury yield curve, plus an applicable credit-adjusted spread
Fair value estimate methodology for notes payable	Indicative market prices and recent trading activity of our notes payable	Indicative market prices and recent trading activity of our notes payable

This item represents the disclosure of the methods and significant assumptions used to estimate the fair value of notes receivables issued in connection with Crest property sales. This item represents management's methodology (for example, procedures or techniques) for estimating the fair value as of the balance sheet date of the notes receivable.

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- Definition

This item represents the disclosure of the methods and significant assumptions used to estimate the fair value of mortgage notes payable. This item represents management's methodology (for example, procedures or techniques) for estimating the fair value as of the balance sheet date of the mortgage notes payable.

+ Details

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- Definition

This item represents the disclosure of the methods and significant assumptions used to estimate the fair value of mortgages payable. This item represents management's methodology (for example, procedures or techniques) for estimating the fair value as of the balance sheet date of the mortgages payable.

+ Details

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents mortgages payable as of the balance sheet date.

+ Details

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- Definition

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-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 SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20, 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19,20,22)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. An amount representing an agreement for an unconditional promise by the maker to pay the Company (holder) a definite sum of money at a future date(s).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 3

-Subparagraph b

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.3(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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