Investments in Real Estate Partnerships - Income Statment Summarized Financial Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Document Fiscal Year Focus	2017
Revenues and expenses for the investments in real estate partnerships on a combined basis
Total revenues	$ 396,596	$ 364,087	$ 363,745
Operating expenses:
Depreciation and amortization	99,327	99,252	111,648
Operating and maintenance	58,283	52,725	51,970
General and administrative	5,582	5,342	5,292
Real estate taxes	49,904	42,813	43,769
Other expenses	2,923	2,356	2,989
Total operating expenses	216,019	202,488	215,668
Other expense (income):
Interest expense, net	73,244	69,193	79,477
Equity Method Investment, Summarized Financial Information, Gain Loss on Sale of Real Estate	34,276	70,907	2,766
Provision for impairment	0	0	9,102
Loss (gain) on extinguishment of debt	0	69	0
Other expense (income)	1,651	2,197	1,516
Total other expense	40,619	552	87,329
Net income (loss)	139,958	161,047	60,748
Unconsolidated Properties [Member]
Other expense (income):
Income (Loss) from Equity Method Investments	$ 34,276	$ 70,907	$ 2,766