Fair Value of Financial Instruments (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Company's estimates of fair value differ from the carrying amounts
Mortgage payable, net of discounts, Carrying Amount	$ 491,867	$ 711,789
Mortgage payable, net of discounts, Fair Value	506,042	726,348
Unsecured notes payable, net of discounts, Carrying Amount	1,572,750	1,274,047
Unsecured notes payable, net of discounts, Fair Value	1,610,233	1,338,743
Variable rate debt instruments, Carrying Amount	427,610	444,610
Variable rate debt instruments, Fair Value	416,089	432,556
Notes receivable, Carrying Amount	32,407	31,216
Notes receivable, Fair Value	$ 32,309	$ 28,921

Company's estimates of fair value differ from the carrying amounts.

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- Definition

Secured Debt Principal Balance Outstanding.

+ Details

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- Definition

Secured Debt Principal Balance Outstanding Fair Value Disclosure.

+ Details

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- Definition

Unsecured notes payable, net of discounts, Carrying Amount.

+ Details

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- Definition

Unsecured notes payable, net of discounts, Fair Value.

+ Details

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- Definition

Variable Rate Debt Instruments, Carrying Amount.

+ Details

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- Definition

Variable Rate Debt Instruments, Fair Value.

+ 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. 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

+ Details

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- Definition

For an unclassified balance sheet, 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). Such amount may include accrued interest receivable in accordance with the terms of the note. The note also may contain provisions and related items including a discount or premium, payable on demand, secured, or unsecured, interest bearing or noninterest bearing, among a myriad of other features and characteristics. This amount does not include amounts related to receivables held-for-sale.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.10(3))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 9

-Section 03

-Paragraph 10

-Subparagraph 3

+ Details

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