Fair Value Measurements (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Fair Value of Financial Instruments
Marketable securities	$ 47,716,000us-gaap_AvailableForSaleSecurities	$ 39,429,000us-gaap_AvailableForSaleSecurities
Interest rate swap agreements (included in other assets)	3,000	2,174,000
Interest rate swap agreements (included in accrued interest payable and other liabilities)	16,983,000	14,728,000
Debt and preferred equity investments	1,548,739,000	1,408,804,000
Carrying Value
Fair Value of Financial Instruments
Fixed rate debt	6,016,084,000	6,140,786,000
Variable rate debt	2,073,000,000	2,291,943,000
Total	8,089,084,000	8,432,729,000
Fair Value
Fair Value of Financial Instruments
Marketable securities	47,716,000	39,429,000
Total	8,698,913,000	8,881,188,000
Estimated fair value of debt and preferred equity investments, low end of range	1,700,000,000	1,500,000,000
Estimated fair value of debt and preferred equity investments, high end of range	1,900,000,000	1,800,000,000
Level 1
Fair Value of Financial Instruments
Interest rate swap agreements (included in other assets)	0	0
Interest rate swap agreements (included in accrued interest payable and other liabilities)	0	0
Level 2
Fair Value of Financial Instruments
Interest rate swap agreements (included in other assets)	3,000	2,174,000
Interest rate swap agreements (included in accrued interest payable and other liabilities)	16,983,000	14,728,000
Level 3
Fair Value of Financial Instruments
Marketable securities	0	0
Interest rate swap agreements (included in other assets)	0	0
Interest rate swap agreements (included in accrued interest payable and other liabilities)	0	0
Level 3 \| Carrying Value
Fair Value of Financial Instruments
Debt and preferred equity investments	1,548,739,000	1,408,804,000
Level 3 \| Fair Value
Fair Value of Financial Instruments
Fixed rate debt	6,582,767,000	6,565,236,000
Variable rate debt	2,116,146,000	2,315,952,000
Equity Securities \| Level 1
Fair Value of Financial Instruments
Marketable securities	4,287,000	4,332,000
Mortgage-backed securities \| Level 2
Fair Value of Financial Instruments
Marketable securities	$ 43,429,000	$ 35,097,000

Represents the high end of the range of estimated fair value for investments in mortgage loans on real estate.

No definition available.

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- Definition

Represents the low end of the range of estimated fair value for investments in mortgage loans on real estate.

+ References

No definition available.

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- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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-Publisher FASB

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-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (a)

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

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- Definition

The fair value amount of long-term debt 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.

+ References

No definition available.

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- Definition

The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a set, unchanging rate.

+ References

No definition available.

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- Definition

The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

+ References

No definition available.

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- Definition

The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(c))

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