Note 18 - Preferred Stock, Common Stock and Convertible Unit Transactions - Outstanding Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Preferred stock, shares authorized (in shares)	7,054,000	7,054,000
Preferred stock, liquidation preference	$ 484,179	$ 485,868
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Series L Preferred Stock [Member]
Preferred stock, shares authorized (in shares)	10,350	10,350
Shares issued and outstanding (in shares)	8,902	8,946
Preferred stock, liquidation preference	$ 222,543	$ 223,637
Dividend rate	5.125%	5.125%
Annual dividend per depository share (in dollars per share)	$ 1.28125	$ 1.28125
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Redemption date	Aug. 16, 2022	Aug. 16, 2022
Series M Preferred Stock [Member]
Preferred stock, shares authorized (in shares)	10,580	10,580
Shares issued and outstanding (in shares)	10,465	10,489
Preferred stock, liquidation preference	$ 261,636	$ 262,231
Dividend rate	5.25%	5.25%
Annual dividend per depository share (in dollars per share)	$ 1.3125	$ 1.3125
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Redemption date	Dec. 20, 2022	Dec. 20, 2022
Redeemable Preferred Stock [Member]
Shares issued and outstanding (in shares)	19,367	19,435
Preferred stock, liquidation preference	$ 484,179	$ 485,868