Real Estate Properties - Summary of Income Statement Information for Properties Sold (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Statements of Operations:
Rental income	$ 167,972	$ 172,040
Tenant reimbursements and other income	45,083	45,220
Total revenues	213,055us-gaap_RealEstateRevenueNet	217,260us-gaap_RealEstateRevenueNet
Operating expenses	97,871	101,731
General and administrative	16,558us-gaap_GeneralAndAdministrativeExpense	24,848us-gaap_GeneralAndAdministrativeExpense
Total expenses	179,032us-gaap_CostsAndExpenses	173,472us-gaap_CostsAndExpenses
Operating income	34,023us-gaap_OperatingIncomeLoss	43,788us-gaap_OperatingIncomeLoss
Interest expense	(29,842)us-gaap_InterestExpense	(37,935)us-gaap_InterestExpense
Income from discontinued operations	0	4,011
Discontinued operations, properties sold
Statements of Operations:
Rental income		7,274
Tenant reimbursements and other income		522
Total revenues		7,796
Operating expenses		3,479
General and administrative		3
Total expenses		3,482
Operating income		4,314
Interest expense		(303)
Income from discontinued operations		$ 4,011

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In accordance with the provisions of their lease agreement, this element represents allowable charges due a landlord from its tenant. In retail store and office building leases, for example, tenant reimbursements may cover items such as taxes, utilities, and common area expenses. It also includes other real estate revenue.

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- Definition

Total costs of sales and operating expenses for the period.

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- Definition

Amount of expense incurred and directly related to generating revenue from leased and rented property or equipment.

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Amount after tax of income (loss) from operations classified as a discontinued operation. Excludes gain (loss) on disposal and provision for gain (loss) until disposal.

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The aggregate total of expenses of managing and administering the affairs of an entity, including affiliates of the reporting entity, which are not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

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Amount of the cost of borrowed funds accounted for as interest expense.

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The net result for the period of deducting operating expenses from operating revenues.

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- Definition

The total amount of revenue recognized for the period from operating leases, including minimum lease revenue, contingent revenue, percentage revenue and sublease revenue.

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- Definition

The aggregate revenue from real estate operations during the reporting period.

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