Note 7 - Redeemable Preferred Stock (Details Textual) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended
	Jun. 30, 2015	Sep. 30, 2021	Dec. 31, 2020
Temporary Equity, Shares Issued (in shares)		363,000	363,000
Temporary Equity, Dividend Rate, Percentage		6.50%	6.50%
Series A Preferred Stock [Member]
Temporary Equity, Shares Issued (in shares)	363,000
Proceeds from Issuance of Preferred Stock and Preference Stock, Before Issuance Costs	$ 363
Temporary Equity, Redemption Price Per Share (in dollars per share)	$ 1,000
Temporary Equity, Dividend Rate, Percentage	6.50%
Convertible Preferred Stock, Shares Issued upon Conversion (in shares)	55.9284
Convertible Preferred Stock, Initial Conversion Price (in dollars per share)	$ 17.88
Convertible Preferred Stock, Redemption Option, Percentage of Par Value	105.00%
Convertible Preferred Stock, Common Stock as Percentage of Conversion Price	150.00%