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, 2022	Dec. 31, 2021
Mortgage and notes payable		$ 1,603.1	$ 1,638.7
Prudential Investment Program [Member]
Mortgage and notes payable		$ 416.0	$ 426.9
Weighted average interest rate		2.30%	2.02%
Weighted average remaining term (Month)	[1]	43 months	45 months 18 days
KIR [Member]
Mortgage and notes payable		$ 468.7	$ 492.6
Weighted average interest rate		2.74%	2.55%
Weighted average remaining term (Month)	[1]	25 months 3 days	27 months 27 days
CPP [Member]
Mortgage and notes payable		$ 83.9	$ 84.2
Weighted average interest rate		2.20%	1.85%
Weighted average remaining term (Month)	[1]	52 months 3 days	55 months
Other Institutional Joint Ventures [Member]
Mortgage and notes payable		$ 233.0	$ 232.9
Weighted average interest rate		2.00%	1.65%
Weighted average remaining term (Month)	[1]	56 months 21 days	59 months 21 days
Other Joint Venture Programs [Member]
Mortgage and notes payable		$ 401.5	$ 402.1
Weighted average interest rate		3.63%	3.58%
Weighted average remaining term (Month)	[1]	80 months 3 days	83 months

[1] Includes extension options