Note 13 - Notes Payable - Notes Payable (Details) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Balance, Net		$ 5,044.2	$ 4,831.8
Weighted Average [Member]
Interest Rate	[1]	3.33%	3.46%
Notes Payable [Member]
Deferred financing costs, net (3)	[2]	$ (55.8)	$ (53.1)
Unsecured Debt [Member]
Gross Balance		5,100.0
Unsecured Debt [Member] | Notes Payable [Member]
Gross Balance		$ 5,100.0	$ 4,684.9
Unsecured Debt [Member] | Notes Payable [Member] | Minimum [Member]
Interest Rate		1.90%	2.70%
Unsecured Debt [Member] | Notes Payable [Member] | Maximum [Member]
Interest Rate		4.45%	4.45%
Line of Credit [Member] | Notes Payable [Member]
Gross Balance		$ 0.0	$ 200.0

[1] Weighted-average interest rate

[2] As of December 31, 2020, the Company had $5.6 million of deferred financing costs, net related to the Credit Facility that are included in Other assets on the Company’s Consolidated Balance Sheets.