Represents the weighted average maturity period of the borrowings of the entity.

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- Definition

Represents the number of public issues of unsecured senior notes.

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- Definition

The number of real estate properties serving as collateral for debt as of the balance sheet date.

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- Definition

The number of units (items of property) under capital lease arrangements.

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Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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-Name Regulation S-X (SX)

-Number 210

-Article 7

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The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

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Interest rate stated in the contractual debt agreement.

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-Name Regulation S-X (SX)

-Number 210

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- Definition

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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Reflects the calculation as of the balance sheet date of the average interest rate weighted by the amount of debt outstanding by type or by instrument at that time.

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- Definition

Amount borrowed under the credit facility as of the balance sheet date.

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

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The effective interest rate at the end of the reporting period.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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The amount of debt that an Entity assumes in acquiring a business or in consideration for an asset received in a noncash (or part noncash) acquisition. Noncash is defined as transactions during a period that affect recognized assets or liabilities but that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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- Definition

The net book value of real estate property held for investment purposes.

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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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- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

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-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

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Indebtedness (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended			9 Months Ended
	Sep. 30, 2011 property segment Y count state	Sep. 30, 2011 property segment Y count state	Sep. 30, 2010	Dec. 31, 2010	Sep. 30, 2011 Unsecured revolving credit facility	Jun. 30, 2011 Unsecured revolving credit facility	Jun. 30, 2011 Previous unsecured revolving credit facility	Sep. 30, 2011 Senior unsecured notes 8.625%	Sep. 30, 2011 Senior unsecured notes 4.30%	Sep. 30, 2011 Senior unsecured notes 6.75%	Sep. 30, 2011 Mortgages property	Sep. 30, 2011 Capital leases property
Indebtedness
Mortgage debt assumed	$ 28,869	$ (76,931)	$ (2,458)
Weighted average interest rate on mortgage debt assumed (as a percent)	6.16%	6.16%
Weighted average maturity period of mortgage debt assumed (in years)	5.3	5.3
Unsecured revolving credit facility, maximum borrowing capacity					750,000	750,000	550,000
Number of public issuances of unsecured senior notes (in counts)	3	3
Principal amount of unsecured senior notes	670,849	670,849		422,880				225,000	250,000	200,000
Interest rate on real estate mortgage loan (as a percent)								8.625%	4.30%	6.75%
Aggregate principal amount of mortgage debt											709,624
Number of properties mortgaged											73
Carrying value of properties	3,691,512	3,691,512		3,222,840							872,574	14,304
Number of properties recorded under capital lease												2
Capital leases												16,562
Interest rate, description					LIBOR
Revolving credit facility, interest rate payable (as a percent)					1.80%
Unsecured revolving credit facility, amount outstanding					210,000
Revolving credit facility, available amount					$ 540,000