Fair Value of Derivatives and Financial Instruments (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes receivable, net	$ 15,494	$ 14,369
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	0
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Derivative Asset	12	88
Derivative Liability	9,109	10,368
Secured debt instruments - variable rate
Borrowings outstanding	2,300	1,900
Unsecured debt instruments
Redeemable Noncontrolling Interest, Equity, Carrying Amount	290,278
Redeemable noncontrolling interests in the Operating Partnership (d)	290,278	282,480
Carrying (Reported) Amount, Fair Value Disclosure [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes receivable, net	15,494	14,369
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Total assets	15,506	14,457
Unsecured debt instruments
Total liabilities	3,573,512	3,593,473
Carrying (Reported) Amount, Fair Value Disclosure [Member] \| Senior Unsecured Notes [Member] \| Fair Value, Measurements, Recurring [Member]
Unsecured debt instruments
Unsecured debt instruments (c)	1,756,964	2,069,076
Estimate of Fair Value, Fair Value Disclosure [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Notes receivable (a)	15,863	14,808
Total assets	15,875	14,896
Unsecured debt instruments
Total liabilities	3,671,647	3,721,512
Redeemable noncontrolling interests in the Operating Partnership (d)	290,278	282,480
Estimate of Fair Value, Fair Value Disclosure [Member] \| Interest Rate Contracts [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Derivatives - Interest rate contracts	12	88
Derivatives - Interest rate contracts (b)	9,109	10,368
Estimate of Fair Value, Fair Value Disclosure [Member] \| Mortgages Notes Payable [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate	420,571	415,663
Secured debt instruments - variable rate
Secured debt instruments - variable rate	31,337	31,337
Estimate of Fair Value, Fair Value Disclosure [Member] \| Tax Exempt Notes Payable [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - variable rate
Secured debt instruments - variable rate	94,700	94,700
Estimate of Fair Value, Fair Value Disclosure [Member] \| Line of Credit [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate	592,916	606,623
Secured debt instruments - variable rate
Secured debt instruments - variable rate	249,378	266,196
Unsecured debt instruments
Unsecured debt instruments (c)		152,500
Estimate of Fair Value, Fair Value Disclosure [Member] \| Senior Unsecured Notes [Member] \| Fair Value, Measurements, Recurring [Member]
Unsecured debt instruments
Unsecured debt instruments (c)	1,816,636	2,144,125
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 1 [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Notes receivable (a)	0	0
Total assets	0	0
Unsecured debt instruments
Total liabilities	0	0
Redeemable noncontrolling interests in the Operating Partnership (d)	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 1 [Member] \| Interest Rate Contracts [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Derivatives - Interest rate contracts	0	0
Derivatives - Interest rate contracts (b)	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 1 [Member] \| Mortgages Notes Payable [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate	0	0
Secured debt instruments - variable rate
Secured debt instruments - variable rate	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 1 [Member] \| Tax Exempt Notes Payable [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - variable rate
Secured debt instruments - variable rate	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 1 [Member] \| Line of Credit [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate	0	0
Secured debt instruments - variable rate
Secured debt instruments - variable rate	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 1 [Member] \| Commercial bank [Member] \| Fair Value, Measurements, Recurring [Member]
Unsecured debt instruments
Unsecured debt instruments (c)	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 1 [Member] \| Senior Unsecured Notes [Member] \| Fair Value, Measurements, Recurring [Member]
Unsecured debt instruments
Unsecured debt instruments (c)	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 2 [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Notes receivable (a)	0	0
Total assets	12	88
Unsecured debt instruments
Total liabilities	9,109	10,368
Redeemable noncontrolling interests in the Operating Partnership (d)	290,278	282,480
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 2 [Member] \| Interest Rate Contracts [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Derivatives - Interest rate contracts	12	88
Derivatives - Interest rate contracts (b)	9,109	10,368
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 2 [Member] \| Mortgages Notes Payable [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate	0	0
Secured debt instruments - variable rate
Secured debt instruments - variable rate	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 2 [Member] \| Tax Exempt Notes Payable [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - variable rate
Secured debt instruments - variable rate	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 2 [Member] \| Line of Credit [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate	0	0
Secured debt instruments - variable rate
Secured debt instruments - variable rate	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 2 [Member] \| Commercial bank [Member] \| Fair Value, Measurements, Recurring [Member]
Unsecured debt instruments
Unsecured debt instruments (c)	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 2 [Member] \| Senior Unsecured Notes [Member] \| Fair Value, Measurements, Recurring [Member]
Unsecured debt instruments
Unsecured debt instruments (c)	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 3 [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Notes receivable (a)	15,863	14,808
Total assets	15,863	14,808
Unsecured debt instruments
Total liabilities	3,662,538	3,711,144
Redeemable noncontrolling interests in the Operating Partnership (d)	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 3 [Member] \| Interest Rate Contracts [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Derivatives - Interest rate contracts	0	0
Derivatives - Interest rate contracts (b)	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 3 [Member] \| Mortgages Notes Payable [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate	420,571	415,663
Secured debt instruments - variable rate
Secured debt instruments - variable rate	31,337	31,337
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 3 [Member] \| Tax Exempt Notes Payable [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - variable rate
Secured debt instruments - variable rate	94,700	94,700
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 3 [Member] \| Line of Credit [Member] \| Fair Value, Measurements, Recurring [Member]
Secured debt instruments - fixed rate
Secured debt instruments - fixed rate	592,916	606,623
Secured debt instruments - variable rate
Secured debt instruments - variable rate	249,378	266,196
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 3 [Member] \| Commercial bank [Member] \| Fair Value, Measurements, Recurring [Member]
Unsecured debt instruments
Unsecured debt instruments (c)	457,000	152,500
Estimate of Fair Value, Fair Value Disclosure [Member] \| Level 3 [Member] \| Senior Unsecured Notes [Member] \| Fair Value, Measurements, Recurring [Member]
Unsecured debt instruments
Unsecured debt instruments (c)	1,816,636	2,144,125
Unsecured Revolving Credit Facility due October 2015 [Member]
Secured debt instruments - variable rate
Borrowings outstanding	457,000	152,500
Variable Rate Debt [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Secured debt including debt on real estate held for sale	375,415	392,233
Variable Rate Debt [Member] \| Tax Exempt Notes Payable [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member] \| Tax Exempt Notes Payable [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Secured debt including debt on real estate held for sale	94,700	94,700
Variable Rate Debt [Member] \| Line of Credit [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member] \| Line of Credit [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Secured debt including debt on real estate held for sale	249,378	266,196
Variable Rate Debt [Member] \| Mortgages Notes Payable [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member] \| Mortgages Notes Payable [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Secured debt including debt on real estate held for sale	31,337	31,337
Fixed Rate Debt [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Secured debt including debt on real estate held for sale	975,024	969,296
Fixed Rate Debt [Member] \| Line of Credit [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member] \| Line of Credit [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Secured debt including debt on real estate held for sale	566,288	568,086
Fixed Rate Debt [Member] \| Mortgages Notes Payable [Member] \| Carrying (Reported) Amount, Fair Value Disclosure [Member] \| Mortgages Notes Payable [Member] \| Fair Value, Measurements, Recurring [Member]
Estimated fair values of the financial instruments either recorded or disclosed on a recurring basis
Secured debt including debt on real estate held for sale	$ 408,736	$ 401,210

Fair Value Assets Measured On Recurring Basis.

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Fair Value Liabilities Measured On Recurring Basis Fixed Rate Secured Debt Instruments.

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Fair Value Liabilities Measured On Recurring Basis Variable Rate Secured Debt Instruments.

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Fair Value Liabilities Measured On Recurring Basis Variable Rate Unsecured Debt Instruments.

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Fair value of fixed rate secured debt instruments as of the balance sheet date.

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Secured debt including debt on real estate held for sale.

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Fair value of unsecured debt instruments as of the balance sheet date.

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Fair value of variable rate secured debt instruments as of the balance sheet date.

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Fair value, after the 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 not subject to a master netting arrangement and not elected to be offset.

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Fair value, after offset of derivative liability, of 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, before offset against an obligation to return collateral under a master netting arrangement. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, after offset of derivative asset, of 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, elected not to be and before offset against a right to receive collateral under a master netting arrangement. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Fair value, after the 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 not subject to a master netting arrangement and not elected to be offset.

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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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Amount of transfer of financial instrument classified as an asset into (out of) level 3 of the fair value hierarchy.

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Fair value of financial and nonfinancial obligations.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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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.

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Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

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As of the reporting date, the aggregate carrying amount of all noncontrolling interests which are redeemable by the (parent) entity (1) at a fixed or determinable price on a fixed or determinable date, (2) at the option of the holder of the noncontrolling interest, or (3) upon occurrence of an event that is not solely within the control of the (parent) entity. This item includes noncontrolling interest holder's ownership (or holders' ownership) regardless of the type of equity interest (common, preferred, other) including all potential organizational (legal) forms of the investee entity.

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