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, 2019	Dec. 31, 2018
Mortgage and notes payable		$ 1,594.1	$ 1,782.6
Prudential Investment Program [Member]
Mortgage and notes payable		$ 538.1	$ 572.6
Weighted average interest rate		3.46%	4.29%
Weighted average remaining term (Year)	[1]	46 years 9 months 18 days	49 years
KIR [Member]
Mortgage and notes payable		$ 556.0	$ 651.4
Weighted average interest rate		4.39%	4.43%
Weighted average remaining term (Year)	[1]	28 months 12 days	40 months 12 days
CPP [Member]
Mortgage and notes payable		$ 84.8	$ 84.4
Weighted average interest rate		3.25%	3.85%
Weighted average remaining term (Year)	[1]	42 months	54 months
Other Joint Venture Programs [Member]
Mortgage and notes payable		$ 415.2	$ 474.2
Weighted average interest rate		3.87%	4.26%
Weighted average remaining term (Year)	[1]	80 months 27 days	78 months 18 days

[1] Average remaining term includes extensions