Note 7 - Investments In and Advances to Real Estate Joint Ventures - Joint Venture Investments Accounted for Under the Equity Method, Debt Details (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Mortgage and notes payable		$ 1,541.0	$ 1,594.1
Prudential Investment Program [Member]
Mortgage and notes payable		$ 495.8	$ 538.1
Weighted average interest rate		2.05%	3.46%
Weighted average remaining term (Month)	[1]	37 months 6 days	46 months 24 days
KIR [Member]
Mortgage and notes payable		$ 536.9	$ 556.0
Weighted average interest rate		3.87%	4.39%
Weighted average remaining term (Month)	[1]	25 months 9 days	28 months 12 days
CPP [Member]
Mortgage and notes payable		$ 84.9	$ 84.8
Weighted average interest rate		3.25%	3.25%
Weighted average remaining term (Month)	[1]	30 months	42 months
Other Joint Venture Programs [Member]
Mortgage and notes payable		$ 423.4	$ 415.2
Weighted average interest rate		3.41%	3.87%
Weighted average remaining term (Month)	[1]	86 months 21 days	80 months 27 days

[1] Average remaining term includes extensions