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		9 Months Ended	12 Months Ended
		Sep. 30, 2020	Dec. 31, 2019
Mortgage and notes payable		$ 1,545.9	$ 1,594.1
Prudential Investment Program [Member]
Mortgage and notes payable		$ 496.9	$ 538.1
Weighted average interest rate		2.06%	3.46%
Weighted average remaining term (Month)	[1]	40 months 9 days	46 months 24 days
KIR [Member]
Mortgage and notes payable		$ 540.6	$ 556.0
Weighted average interest rate		4.00%	4.39%
Weighted average remaining term (Month)	[1]	26 months 21 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]	33 months	42 months
Other Joint Venture Programs [Member]
Mortgage and notes payable		$ 423.5	$ 415.2
Weighted average interest rate		3.45%	3.87%
Weighted average remaining term (Month)	[1]	86 months 6 days	80 months 27 days

[1] Includes extension options