Investments in Real Estate Partnerships - Income Statment Summarized Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues and expenses for the investments in real estate partnerships on a combined basis
Total revenues	$ 258,460	$ 242,944	$ 231,113	$ 283,658	$ 288,733	$ 282,276	$ 275,872	$ 286,257	$ 1,016,175	$ 1,133,138	$ 1,120,975
Operating expenses:
Depreciation and amortization									101,590	97,844	99,847
Operating and maintenance									65,146	65,811	66,299
General and administrative									5,870	6,201	5,697
Real estate taxes									53,747	53,410	54,119
Other operating expenses									3,126	2,709	2,700
Total operating expenses									229,479	225,975	228,662
Other expense (income):
Interest expense, net									66,786	75,449	73,508
Equity Method Investment, Summarized Financial Information, Gain Loss on Sale of Real Estate									(7,146)	(64,798)	(16,624)
Early extinguishment of debt									554	0	0
Provision for impairment, net of tax									0	9,223	0
Total other expense (income)									60,194	19,874	56,884
Net income									47,317	243,258	252,325
Revenues [Member]
Revenues and expenses for the investments in real estate partnerships on a combined basis
Total revenues									381,094	417,053	414,631
Net Income [Member]
Other expense (income):
Net income									91,421	171,204	129,085
Unconsolidated Properties [Member]
Other expense (income):
Income (Loss) from Equity Method Investments									$ 34,169	$ 60,956	$ 42,974