Represents the net gain or loss on all cash flow hedges that is recognized in accumulated other comprehensive income.

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Derivative and Other Fair Value Instruments.

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Represents the number of fair value or cash flow hedges that were terminated in conjunction with the issuance of long-term debt.

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- Definition

Represents accumulated other comprehensive losses that may be recognized as additional interest expense in the statement of operations during the twelve months subsequent to the balance sheet date.

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Aggregate notional amount of derivative designated as cash flow hedging instruments with mandatory counterparty terminations designated for year one maturity. The notional amount relates to a number of currency units, shares, bushels, pounds, or other units specified in a derivative instrument.

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Aggregate notional amount of derivative designated as cash flow hedging instruments with mandatory counterparty terminations designated for year three maturity. The notional amount relates to a number of currency units, shares, bushels, pounds, or other units specified in a derivative instrument.

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Aggregate notional amount of derivative designated as cash flow hedging instruments with mandatory counterparty terminations designated for year two maturity. The notional amount relates to a number of currency units, shares, bushels, pounds, or other units specified in a derivative instrument.

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- Definition

Date when the notes are scheduled to be fully repaid, which may be presented in a variety of ways (year, month and year, day, month and year, quarter, etc.).

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Estimated fair value of the mortgage notes payable at the balance sheet date.

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Estimated fair value of the unsecured notes payable at the balance sheet date.

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- Definition

The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

+ References

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

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16, 20

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- Definition

Interest rate stated in the contractual debt agreement.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

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Amount as of the balance sheet date of the unamortized adjustment to the carrying value of an interest-bearing hedged item made under an effective interest rate fair value hedge that must be amortized upon discontinuation of the interest rate fair value hedge.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 24

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance-sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20, 22

-Article 5

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 13, 16

-Article 9

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The cash outflow (inflow) for a financial contract that meets the hedge criteria as either a cash flow hedge, fair value hedge, or hedge of a net investment in a foreign operation.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 14

-Subparagraph FN4

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The cash inflow associated with the aggregate amount received by the entity through sale or maturity of marketable securities (trading, held-to-maturity, or available-for-sale) during the period.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 15

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-Name Statement of Financial Accounting Standard (FAS)

-Number 95

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 16

-Subparagraph a

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The net realized gains or losses on investments during the period.

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 3

-Subparagraph a

-Article 7

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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.

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Derivative and Other Fair Value Instruments (Details Textuals) (USD $)	12 Months Ended			1 Months Ended	3 Months Ended			12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Jun. 30, 2009	Jul. 31, 2010 Forward Starting Swaps [Member]	Jun. 30, 2009 Forward Starting Swaps [Member]	Dec. 31, 2008 Treasury Locks [Member]	Mar. 31, 2008 Treasury Locks [Member]	Dec. 31, 2009 Treasury Locks [Member]	Dec. 31, 2010 4.75% Interest Rate Debt [Member]	Dec. 31, 2009 4.75% Interest Rate Debt [Member]	Jul. 31, 2010 10 year fixed Interest Rate Notes [Member]
Derivative [Line Items]
Receipt on discontinuation of cash flow hedge		$ 400,000		$ 10,000,000				$ 10,800,000
Discontinuation of cash flow hedge number of contract					6	6	3
Convertible Notes, stated interest rate		5.60%							4.75%	4.75%
Maturity period of interest rate notes									ten years
Mortgage loan issued	650,000,000								600,000,000		600,000,000
Derivative and Other Fair Value Instruments (Textuals) [Abstract]
Mortgage notes payable	4,762,896,000	4,783,446,000
Notes, net	5,185,180,000	4,609,124,000
Fair value of mortgage notes payable	4,700,000,000	4,600,000,000
Fair value of unsecured notes payable including line of credit	5,500,000,000	4,700,000,000
Forward starting swaps counterparty terminations designated for 2011 maturity	350,000,000
Forward starting swaps counterparty terminations designated for 2012 maturity	400,000,000
Forward starting swaps counterparty terminations designated for 2013 maturity	200,000,000
Deferred Gains In OCI	58,300,000	4,200,000
Estimated Future Losses In OCI	5,600,000
Reduction in interest expenses, deferred			200,000
Proceeds from sale of investment securities	25,000,000	215,753,000
Gain on sale of investment securities		$ 4,943,000