Fair Value of Financial Instruments Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Company's estimates of fair value differ from the carrying amounts
Mortgage notes payable, Carrying Amount	$ 438,404	$ 443,942
Mortgage notes payable, Fair Value	474,036	486,412
Unsecured Notes Payable, Carrying Amount	1,418,548	1,430,343
Unsecured Notes Payable, Fair Value	1,495,998	1,553,123
Variable Rate Debt, Carrying Amount	528,610	597,610
Variable Rate Debt, Fair Value	526,693	595,693
Notes Receivable, Carrying Amount	7,026	7,226
Notes Receivable, Fair Value	$ 7,080	$ 7,783

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Secured Debt Principal Balance Outstanding.

+ References

No definition available.

+ Details

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- Definition

Secured Debt Principal Balance Outstanding Fair Value Disclosure.

+ References

No definition available.

+ Details

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- Definition

Unsecured notes payable, net of discounts, Carrying Amount.

+ References

No definition available.

+ Details

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- Definition

Unsecured notes payable, net of discounts, Fair Value.

+ References

No definition available.

+ Details

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- Definition

Variable Rate Debt Instruments, Carrying Amount.

+ References

No definition available.

+ Details

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- Definition

Variable Rate Debt Instruments, Fair Value.

+ References

No definition available.

+ 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 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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 3

-Subparagraph b

-Article 5

+ Details

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- Definition

Amount representing an agreement for an unconditional promise by the maker to pay the entity (holder) a definite sum of money at a future date. 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. Excludes 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

-Section 03

-Paragraph 10

-Subparagraph 3

-Article 9

+ Details

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