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		6 Months Ended	12 Months Ended
		Jun. 30, 2020	Dec. 31, 2019
Mortgage and notes payable		$ 1,603.1	$ 1,594.1
Prudential Investment Program [Member]
Mortgage and notes payable		$ 535.6	$ 538.1
Weighted average interest rate		2.31%	3.46%
Weighted average remaining term (Year)	[1]	40 years 8 months 12 days	46 years 9 months 18 days
KIR [Member]
Mortgage and notes payable		$ 558.5	$ 556.0
Weighted average interest rate		4.04%	4.39%
Weighted average remaining term (Year)	[1]	29 months	28 months 12 days
CPP [Member]
Mortgage and notes payable		$ 84.8	$ 84.8
Weighted average interest rate		3.25%	3.25%
Weighted average remaining term (Year)	[1]	36 months	42 months
Other Joint Venture Programs [Member]
Mortgage and notes payable		$ 424.2	$ 415.2
Weighted average interest rate		3.45%	3.87%
Weighted average remaining term (Year)	[1]	89 months 3 days	80 months 27 days

[1] Includes extension options