Investments in Real Estate Partnerships - Income Statment Summarized Financial Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) property	Dec. 31, 2014 USD ($) property	Dec. 31, 2013 USD ($) property
Schedule of Equity Method Investments [Line Items]
Document Fiscal Year Focus	2015
Proceeds from sale of real estate investments	$ 108,822	$ 118,787	$ 212,632
Revenues and expenses for the investments in real estate partnerships on a combined basis
Total revenues	363,745	361,103	378,670
Operating expenses:
Depreciation and amortization	111,648	117,780	125,363
Operating and maintenance	51,970	55,216	55,423
General and administrative	5,292	5,503	7,385
Real estate taxes	43,769	42,380	45,451
Other expenses	2,989	2,234	1,725
Total operating expenses	215,668	223,113	235,347
Other expense (income):
Interest expense, net	79,477	84,155	95,505
Gain on sale of real estate	2,766	28,856	15,695
Loss (gain) on extinguishment of debt	0	114	(1,780)
Provision for impairment	9,102	2,123	0
Preferred return on equity investment	0	0	(4,499)
Other expense (income)	1,516	988	(1,258)
Total other expense	87,329	58,524	72,273
Net income (loss)	60,748	79,466	71,050
Income (Loss) from Equity Method Investments	22,508	31,270	31,718
Unconsolidated Properties [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds from sale of real estate investments	39,459	88,106	145,295
Gain on sale of real estate investments [Member]
Other expense (income):
Income (Loss) from Equity Method Investments	$ 1,108	$ 13,615	$ 3,847
Operating Segments [Member]
Other expense (income):
Number of Real Estate Properties Sold | property	5	11	12
Operating Segments [Member] | Unconsolidated Properties [Member]
Other expense (income):
Number of Real Estate Properties Sold | property	2	6	15
Land [Member]
Other expense (income):
Number of Real Estate Properties Sold | property	2	6	10
Land [Member] | Unconsolidated Properties [Member]
Other expense (income):
Number of Real Estate Properties Sold | property	0	2	3