Investments in Real Estate Partnerships - Income Statment Summarized Financial Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]
Document Fiscal Year Focus	2014
Proceeds from sale of real estate investments	$ 118,787	$ 212,632	$ 352,707
Revenues and expenses for the investments in real estate partnerships on a combined basis
Total revenues	361,103	378,670	387,908
Operating expenses:
Depreciation and amortization	117,780	125,363	128,946
Operating and maintenance	55,216	55,423	55,394
General and administrative	5,503	7,385	7,549
Real estate taxes	42,380	45,451	46,395
Other expenses	2,234	1,725	3,521
Total operating expenses	223,113	235,347	241,805
Other expense (income):
Interest expense, net	84,155	95,505	104,694
Gain on sale of real estate	28,856	15,695	40,437
Loss (gain) on extinguishment of debt	114	(1,780)	967
Provision for impairment	2,123	0	3,775
Preferred return on equity investment	0	(4,499)	(2,211)
Other expense (income)	988	(1,258)	51
Total other expense	58,524	72,273	66,839
Net income (loss)	79,466	71,050	79,264
Income (Loss) from Equity Method Investments	31,270	31,718	23,807
Unconsolidated Properties [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds from sale of real estate investments	88,106	145,295	119,275
Gain on sale of real estate investments [Member]
Other expense (income):
Income (Loss) from Equity Method Investments	$ 13,615	$ 3,847	$ 8,962
Operating Segments [Member]
Other expense (income):
Number of Real Estate Properties Sold	11	12	20
Operating Segments [Member] | Unconsolidated Properties [Member]
Other expense (income):
Number of Real Estate Properties Sold	6	15	7
Land [Member]
Other expense (income):
Number of Real Estate Properties Sold	6	10	7
Land [Member] | Unconsolidated Properties [Member]
Other expense (income):
Number of Real Estate Properties Sold	2	3	1