Note 16 - Preferred Stock, Common Stock and Convertible Unit Transactions (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Schedule of Stockholders Equity [Table Text Block]

As of December 31, 2019
Class of Preferred Stock	Shares Authorized		Shares Issued and Outstanding		Liquidation Preference (in thousands)		Dividend Rate			Annual Dividend per Depositary Share		Par Value		Optional Redemption Date
Class L		10,350		9,000	$	225,000		5.125	%	$	1.28125	$	1.00	8/16/2022
Class M		10,580		10,580		264,500		5.250	%	$	1.31250	$	1.00	12/20/2022
				19,580	$	489,500

As of December 31, 2018
Class of Preferred Stock	Shares Authorized		Shares Issued and Outstanding		Liquidation Preference (in thousands)		Dividend Rate			Annual Dividend per Depositary Share		Par Value		Optional Redemption Date
Class I		18,400		7,000	$	175,000		6.000	%	$	1.50000	$	1.00	3/20/2017
Class J		9,000		9,000		225,000		5.500	%	$	1.37500	$	1.00	7/25/2017
Class K		8,050		7,000		175,000		5.625	%	$	1.40625	$	1.00	12/7/2017
Class L		10,350		9,000		225,000		5.125	%	$	1.28125	$	1.00	8/16/2022
Class M (1)		10,580		10,580		264,500		5.250	%	$	1.31250	$	1.00	12/20/2022
				42,580	$	1,064,500

Dividends Declared [Table Text Block]

	Year Ended December 31,
	2019		2018		2017
Common Stock	$	1.12000	$	1.12000	$	1.09000
Class I Depositary Shares	$	0.99583	$	1.50000	$	1.50000
Class I Depositary Shares Redeemed	$	-	$	-	$	0.96250
Class J Depositary Shares	$	1.37500	$	1.37500	$	1.37500
Class K Depositary Shares	$	0.93359	$	1.40625	$	1.40625
Class L Depositary Shares	$	1.28125	$	1.28125	$	0.48047
Class M Depositary Shares	$	1.31250	$	1.31250	$	0.04010

Preferred Stock Redeemed [Member]

Notes Tables

Schedule of Stockholders Equity [Table Text Block]

Class of Preferred Stock	Redemption Date	Depositary Shares Redeemed		Redemption Price per Depositary Share		Redemption Amount (in millions)		Redemption Charges (in millions) (1)
Class J	12/31/2019		9,000,000	$	25.00	$	225.0	$	7.1
Class I	9/14/2019		7,000,000	$	25.00	$	175.0	$	5.5
Class K	9/14/2019		7,000,000	$	25.00	$	175.0	$	5.9