Note 4 - Investments In and Advances to Real Estate Joint Ventures - Joint Venture Investments Accounted for Under the Equity Method, Debt Details (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2021	Dec. 31, 2020
Mortgage and notes payable		$ 1,486.6	$ 1,541.0
Prudential Investment Program [Member]
Mortgage and notes payable		$ 494.6	$ 495.8
Weighted average interest rate		2.03%	2.05%
Weighted average remaining term (Month)	[1]	34 months 6 days	37 months 6 days
KIR [Member]
Mortgage and notes payable		$ 524.3	$ 536.9
Weighted average interest rate		3.27%	3.87%
Weighted average remaining term (Month)	[1]	28 months 27 days	25 months 9 days
CPP [Member]
Mortgage and notes payable		$ 85.0	$ 84.9
Weighted average interest rate		3.25%	3.25%
Weighted average remaining term (Month)	[1]	27 months	30 months
Other Joint Venture Programs [Member]
Mortgage and notes payable		$ 382.7	$ 423.4
Weighted average interest rate		3.59%	3.41%
Weighted average remaining term (Month)	[1]	89 months 24 days	86 months 21 days

[1] Includes extension options