Investments in Real Estate Partnerships - Scheduled Principal Payments (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 43,549,000
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Two	95,964,000
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Three	152,691,000
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Four	393,396,000
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Five	219,072,000
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal After Year Five	910,719,000
Unamortized debt premiums, net	1,257,000
Equity Method Investment, Summarized Financial Information, Notes Payable	1,816,648,000	1,874,780,000
2013	24,191,000
2014	184,382,000
2015	418,181,000
2016	189,648,000
2017	488,959,000
Beyond 5 Years	632,764,000
Unamortized debt discounts (premiums)	3,766,000
Long-term Debt	1,941,891,000	1,982,440,000
Scheduled Principal Payments [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	19,176,000
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Two	21,289,000
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Three	21,895,000
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Four	19,139,000
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Five	18,437,000
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal After Year Five	77,039,000
Unamortized debt premiums, net	0
Equity Method Investment, Summarized Financial Information, Notes Payable	176,975,000
2013	7,872,000
2014	7,383,000
2015	5,746,000
2016	5,487,000
2017	4,584,000
Beyond 5 Years	20,021,000
Unamortized debt discounts (premiums)	0
Long-term Debt	51,093,000
Mortgage Loan Maturities [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	24,373,000
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Two	53,015,000
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Three	130,796,000
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Four	374,257,000
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Five	200,635,000
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal After Year Five	833,680,000
Unamortized debt premiums, net	1,257,000
Equity Method Investment, Summarized Financial Information, Notes Payable	1,618,013,000
2013	16,319,000
2014	26,999,000
2015	62,435,000
2016	14,161,000
2017	84,375,000
Beyond 5 Years	212,743,000
Unamortized debt discounts (premiums)	5,830,000
Long-term Debt	422,862,000
Unsecured Maturities [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	0
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Two	21,660,000
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Three	0
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Four	0
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Five	0
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal After Year Five	0
Unamortized debt premiums, net	0
Equity Method Investment, Summarized Financial Information, Notes Payable	21,660,000
2013	0
2014	150,000,000
2015	350,000,000
2016	170,000,000
2017	400,000,000
Beyond 5 Years	400,000,000
Unamortized debt discounts (premiums)	(2,064,000)
Long-term Debt	1,467,936,000
Equity Method Investments [Member]
Schedule of Equity Method Investments [Line Items]
2013	15,949,000
2014	27,254,000
2015	49,619,000
2016	127,888,000
2017	51,610,000
Beyond 5 Years	325,272,000
Unamortized debt discounts (premiums)	(169,000)
Long-term Debt	$ 597,423,000