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

12 Months Ended

Dec. 31, 2018

Notes Tables

Schedule of Stockholders Equity [Table Text Block]

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		10,580		10,580		264,500		5.250	%	$	1.31250	$	1.00	12/20/2022
				42,580	$	1,064,500

As of December 31, 2017
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		10,580		9,200		230,000		5.250	%	$	1.31250	$	1.00	12/20/2022
				41,200	$	1,030,000

Dividends Declared [Table Text Block]

	Year Ended December 31,
	2018		2017		2016
Common Stock	$	1.12000	$	1.09000	$	1.03500
Class I Depositary Shares	$	1.50000	$	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	$	1.40625	$	1.40625	$	1.40625
Class L Depositary Shares	$	1.28125	$	0.48047	$	-
Class M Depositary Shares	$	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		Redemption Amount (in millions)		Redemption Charges (in millions) (1)
Class I (2)	9/6/2017		9,000,000	$	25.00	$	225.0	$	7.0

Preferred Stock Issued [Member]

Notes Tables

Schedule of Stockholders Equity [Table Text Block]

Class of Preferred Stock	Date Issued	Depositary Shares Issued		Fractional Interest per Share	Net Proceeds, Before Expenses (in millions)		Offering Price
Class L	8/16/2017		9,000,000	1/1000	$	218.1		25.00
Class M (1)	12/20/2017		9,200,000	1/1000	$	222.8		25.00