Note 12 - Notes Payable - Notes Payable (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Balance, Net		$ 4,381.5	$ 4,596.1
Weighted Average [Member]
Interest Rate	[1]	3.48%	3.70%
Notes Payable [Member]
Deferred financing costs, net		$ (53.4)	$ (61.9)
Unsecured Debt [Member]
Total		4,434.9
Unsecured Debt [Member] | Notes Payable [Member]
Total		$ 4,334.9	$ 4,650.0
Unsecured Debt [Member] | Notes Payable [Member] | Minimum [Member]
Interest Rate		2.70%	2.70%
Unsecured Debt [Member] | Notes Payable [Member] | Maximum [Member]
Interest Rate		4.45%	6.88%
Line of Credit [Member] | Notes Payable [Member]
Total		$ 100.0	$ 8.0

[1] Weighted-average interest rate