Investments in Real Estate Partnerships - Scheduled Principal Payments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	$ 79,488
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Two	322,211
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Three	116,362
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Four	85,717
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Five	83,873
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal After Year Five	776,449
Unamortized debt premiums, net	(1,310)
Equity Method Investment, Summarized Financial Information, Notes Payable	1,462,790	1,519,943
2013	432,483
2014	47,577
2015	521,606
2016	61,810
2017	184,443
Beyond 5 Years	768,686
Unamortized debt discounts (premiums)	4,752
Long-term Debt	2,021,357us-gaap_LongTermDebt	1,854,697us-gaap_LongTermDebt
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	19,685
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Two	17,135
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Three	17,517
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Four	18,696
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Five	17,934
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal After Year Five	34,827
Unamortized debt premiums, net	0
Equity Method Investment, Summarized Financial Information, Notes Payable	125,794
2013	6,587
2014	6,135
2015	5,399
2016	4,452
2017	3,443
Beyond 5 Years	22,647
Unamortized debt discounts (premiums)	0
Long-term Debt	48,663
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	59,803
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Two	305,076
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Three	77,385
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Four	67,021
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Five	65,939
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal After Year Five	741,622
Unamortized debt premiums, net	(1,310)
Equity Method Investment, Summarized Financial Information, Notes Payable	1,315,536
2013	75,896
2014	41,442
2015	116,207
2016	57,358
2017	106,000
Beyond 5 Years	96,039
Unamortized debt discounts (premiums)	7,227
Long-term Debt	500,169
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	0
Equity Method Investment, Summarized Financial Information, Long-term Debt, Maturities, Repayments of Principal in Year Three	21,460
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	21,460
2013	350,000
2014	0
2015	400,000
2016	0
2017	75,000
Beyond 5 Years	650,000
Unamortized debt discounts (premiums)	(2,475)
Long-term Debt	1,472,525
Equity Method Investments [Member]
Schedule of Equity Method Investments [Line Items]
Notes payable (note 9)	506,800
2013	24,292
2014	113,155
2015	26,214
2016	27,655
2017	21,618
Beyond 5 Years	294,463
Unamortized debt discounts (premiums)	(617)
Long-term Debt	$ 506,780

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