Segment Information (Reconciliation of Consolidated Net Operating Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Consolidated net operating income	$ 89,708us-gaap_GrossProfit	$ 90,140us-gaap_GrossProfit
Other income (expense):
Depreciation and amortization	(51,111)us-gaap_DepreciationAndAmortization	(52,570)us-gaap_DepreciationAndAmortization
General and administrative expenses	(8,636)us-gaap_GeneralAndAdministrativeExpense	(8,181)us-gaap_GeneralAndAdministrativeExpense
Interest income	750us-gaap_InterestIncomeOther	385us-gaap_InterestIncomeOther
Interest expense	(28,176)us-gaap_InterestExpenseDebt	(31,844)us-gaap_InterestExpenseDebt
Interest expense — amortization of deferred financing costs	(1,079)us-gaap_AmortizationOfFinancingCosts	(1,189)us-gaap_AmortizationOfFinancingCosts
Interest expense — financing obligation	(286)us-gaap_InterestExpenseOther	(272)us-gaap_InterestExpenseOther
Equity in income of Real Estate Ventures	131	242
Net gain on disposition of real estate	9,019	0
Gain on sale of undepreciated real estate	0	1,187
Loss on real estate venture transactions	0	(135)
Provision for impairment on assets held for sale	(1,726)	0
Income (Loss) from continuing operations	8,594	(2,237)
Total discontinued operations	0	(8)
Net income	$ 8,594us-gaap_ProfitLoss	$ (2,245)us-gaap_ProfitLoss

Net Gain (Loss) On Real Estate Venture Transactions, including real estate venture formation

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Net gain (loss) on sale of undepreciated real estate

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Amount of noncash expense included in interest expense to issue debt and obtain financing associated with the related debt instruments. Alternate captions include noncash interest expense.

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The gain (loss) resulting from the sale of a disposal group that is not a discontinued operation. It is included in income from continuing operations before income taxes in the income statement.

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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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This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses and taxes from ongoing operations before extraordinary items, and noncontrolling interest.

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Amount of income (loss) from a disposal group, net of income tax before extraordinary items allocable to noncontrolling interests. Includes, net of tax, income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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

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The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

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