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Investments in and Advances to Other Real Estate Partnerships - Condensed Combined Statements of Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Condensed Combined Statements of Operations [Line Items]
Total Revenues	$ 78,777us-gaap_RealEstateRevenueNet	$ 76,210us-gaap_RealEstateRevenueNet	$ 74,082us-gaap_RealEstateRevenueNet	$ 73,536us-gaap_RealEstateRevenueNet	$ 71,540us-gaap_RealEstateRevenueNet	$ 69,377us-gaap_RealEstateRevenueNet	$ 70,019us-gaap_RealEstateRevenueNet	$ 68,791us-gaap_RealEstateRevenueNet	$ 302,605us-gaap_RealEstateRevenueNet	$ 279,727us-gaap_RealEstateRevenueNet	$ 266,155us-gaap_RealEstateRevenueNet
Property Expenses									(101,533)	(91,692)	(85,530)
Impairment of Real Estate									0	0	20
Depreciation and Other Amortization									(99,949)us-gaap_DepreciationAndAmortization	(95,060)us-gaap_DepreciationAndAmortization	(97,318)us-gaap_DepreciationAndAmortization
Interest Income									2,189us-gaap_InvestmentIncomeInterest	2,438us-gaap_InvestmentIncomeInterest	2,940us-gaap_InvestmentIncomeInterest
Interest Expense									(67,509)us-gaap_InterestExpense	(68,857)us-gaap_InterestExpense	(77,794)us-gaap_InterestExpense
Amortization of Deferred Financing Costs									(2,940)us-gaap_AmortizationOfFinancingCosts	(3,038)us-gaap_AmortizationOfFinancingCosts	(3,252)us-gaap_AmortizationOfFinancingCosts
Loss from Retirement of Debt									(522)	(6,423)	(9,684)
Income (Loss) from Continuing Operations	8,043	10,145	3,281	4,218	2,284	4,958	(1,548)	299	25,687	5,993	(25,181)
Discontinued Operations:
Income (Loss) Attributable to Discontinued Operations									1,785	1,963	6,228
Gain on Sale of Real Estate									23,796	32,657	12,758
Income from Discontinued Operations	11,702	12,073	946	860	19,809	3,559	12,941	(1,689)	25,581	34,620	18,986
Gain on Sale of Real Estate									(83)	1,030	3,777
Net Income (Loss)	19,662us-gaap_ProfitLoss	22,218us-gaap_ProfitLoss	4,227us-gaap_ProfitLoss	5,078us-gaap_ProfitLoss	22,430us-gaap_ProfitLoss	8,738us-gaap_ProfitLoss	11,393us-gaap_ProfitLoss	(1,128)us-gaap_ProfitLoss	51,185us-gaap_ProfitLoss	41,433us-gaap_ProfitLoss	(2,418)us-gaap_ProfitLoss
Other Real Estate Partnerships
Schedule Of Condensed Combined Statements of Operations [Line Items]
Total Revenues									41,994	38,727	38,362
Property Expenses									(12,966)	(12,022)	(10,987)
Impairment of Real Estate									0	0	172
Depreciation and Other Amortization									(11,948)	(11,891)	(13,543)
Interest Income									1,309	4,999	7,776
Interest Expense									(4,669)	(4,701)	(5,712)
Amortization of Deferred Financing Costs									(158)	(187)	(208)
Loss from Retirement of Debt									(133)	(214)	0
Income (Loss) from Continuing Operations									13,429	14,711	15,860
Discontinued Operations:
Income (Loss) Attributable to Discontinued Operations									50	259	(126)
Gain on Sale of Real Estate									2,192	1,687	(93)
Income from Discontinued Operations									2,242	1,946	(219)
Gain on Sale of Real Estate									0	70	0
Net Income (Loss)									$ 15,671	$ 16,727	$ 15,641