Note 17 - Preferred Stock, Common Stock and Convertible Unit Transactions - Preferred Stock Redeemed (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Redemption Charges		$ (0)	$ 18,528	$ (0)
Series J Preferred Stock [Member]
Depositary Shares Redeemed (in shares)			9,000,000
Redemption Price (in dollars per share)			$ 25.00
Redemption Amount			$ 225,000
Redemption Charges	[1]		$ 7,100
Series I Preferred Stock [Member]
Depositary Shares Redeemed (in shares)			7,000,000
Redemption Price (in dollars per share)			$ 25.00
Redemption Amount			$ 175,000
Redemption Charges	[1]		$ 5,500
Series K Preferred Stock [Member]
Depositary Shares Redeemed (in shares)			7,000,000
Redemption Price (in dollars per share)			$ 25.00
Redemption Amount			$ 175,000
Redemption Charges	[1]		$ 5,900

[1] Redemption charges resulting from the difference between the redemption amount and the carrying amount of the respective preferred stock class on the Company's Condensed Consolidated Balance Sheets are accounted for in accordance with the FASB's guidance on Distinguishing Liabilities from Equity. These charges were subtracted from net income attributable to the Company to arrive at net income available to the Company's common shareholders and used in the calculation of earnings per share.