Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Company's estimates of fair value differ from the carrying amounts
Secured Debt	$ 654,590us-gaap_SecuredDebt	$ 670,151us-gaap_SecuredDebt
Mortgage notes payable, Fair Value	707,241	715,244
Unsecured notes payable, Carrying Amount	1,518,108	1,396,620
Unsecured notes payable, Fair Value	1,593,212	1,471,041
Variable rate debt instruments, Carrying Amount	278,610	528,610
Variable rate debt instruments, Fair Value	257,188	526,693
Notes receivable, Carrying Amount	88,000us-gaap_NotesReceivableGross	7,026us-gaap_NotesReceivableGross
Notes receivable, Fair Value	$ 87,692	$ 7,759

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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

Fair value portion of an agreement for an unconditional promise by the maker to pay the holder a definite sum of money at a future date.

+ 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

+ Details

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- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ 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 210.9-03.16)

-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 16

-Article 9

Reference 3: 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 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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