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, 2020	Dec. 31, 2019
Mortgage and notes payable		$ 1,597.7	$ 1,594.1
Prudential Investment Program [Member]
Mortgage and notes payable		$ 537.0	$ 538.1
Weighted average interest rate		2.91%	3.46%
Weighted average remaining term (Year)	[1]	43 years 9 months 18 days	46 years 9 months 18 days
KIR [Member]
Mortgage and notes payable		$ 561.4	$ 556.0
Weighted average interest rate		4.15%	4.39%
Weighted average remaining term (Year)	[1]	32 months	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 (Year)	[1]	39 months	42 months
Other Joint Venture Programs [Member]
Mortgage and notes payable		$ 414.4	$ 415.2
Weighted average interest rate		3.62%	3.87%
Weighted average remaining term (Year)	[1]	78 months 15 days	80 months 27 days

[1] Includes extension options