Real Estate Properties - Schedule of Disposal Groups, Including Discontinued Operations, Balance Sheet and Additional Disclosures (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Balance Sheets:
Real estate properties	$ 5,728,443	$ 5,537,165
Acquired real estate leases	171,503us-gaap_FiniteLivedIntangibleAssetsNet
Rents receivable, net	248,101us-gaap_AccountsReceivableNet	223,769us-gaap_AccountsReceivableNet
Other assets, net	220,480us-gaap_OtherAssets	188,675us-gaap_OtherAssets
Properties held for sale	0us-gaap_InventoryRealEstateHeldForSale	573,531us-gaap_InventoryRealEstateHeldForSale
Mortgage notes payable, net	609,249us-gaap_SecuredDebt	914,510us-gaap_SecuredDebt
Assumed real estate lease obligations	26,784us-gaap_OffMarketLeaseUnfavorable	33,935us-gaap_OffMarketLeaseUnfavorable
Rent collected in advance	31,359us-gaap_DeferredRevenue	27,553us-gaap_DeferredRevenue
Security deposits	14,044us-gaap_SecurityDepositLiability	11,976us-gaap_SecurityDepositLiability
Liabilities related to properties held for sale	0us-gaap_LiabilitiesOfAssetsHeldForSale	28,734us-gaap_LiabilitiesOfAssetsHeldForSale
Real estate properties held for sale
Balance Sheets:
Real estate properties		536,552
Acquired real estate leases		6,937
Rents receivable, net		14,180
Other assets, net		15,862
Properties held for sale		573,531
Mortgage notes payable, net		20,018
Assumed real estate lease obligations		2,070
Rent collected in advance		4,043
Security deposits		2,603
Liabilities related to properties held for sale		$ 28,734

For an unclassified balance sheet, the amount due from customers or clients for goods or services that have been delivered or sold in the normal course of business, reduced to their estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

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Amount of deferred revenue as of balance sheet date. Deferred revenue represents collections of cash or other assets related to a revenue producing activity for which revenue has not yet been recognized. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Represents properties which were acquired directly or through foreclosure for which a committed plan to sell exists and an active program to market such properties has been initiated.

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Liability (such as a mortgage) related to a disposal group that is held for sale and anticipated to be sold in less than one year. The liability is expected to be discharged as part of the plan of sale for the asset.

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This element represents a liability associated with the acquisition of an off-market lease when the terms of the lease are unfavorable to the market terms for the lease at the date of acquisition.

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The aggregate carrying amounts, as of the balance sheet date, of assets not separately disclosed in the balance sheet.

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- Definition

Amount of real estate investment property which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; and (7) other real estate investments.

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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

This element represents money paid in advance to protect the provider of a product or service, such as a lessor, against damage or nonpayment by the buyer or tenant (lessee) during the term of the agreement. Such damages may include physical damage to the property, theft of property, and other contractual breaches. Security deposits held may be interest or noninterest bearing.

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