Note 7 - Stockholders' Equity - Common Stock Dividend Policy (Details)	9 Months Ended
	Sep. 30, 2021 $ / shares
Quarterly Average Realized Price, Level 1 [Member]
Quarterly dividend per share (in dollars per share)	$ 0.0025
Annual dividend per share (in dollars per share)	0.01
Minimum annual component per share (in dollars per share)	0.015
Annualized dividends (in dollars per share)	0.025
Quarterly Average Realized Price, Level 2 [Member]
Quarterly dividend per share (in dollars per share)	0.01
Annual dividend per share (in dollars per share)	0.04
Minimum annual component per share (in dollars per share)	0.015
Annualized dividends (in dollars per share)	0.055
Quarterly Average Realized Price, Level 3 [Member]
Quarterly dividend per share (in dollars per share)	0.015
Annual dividend per share (in dollars per share)	0.06
Minimum annual component per share (in dollars per share)	0.015
Annualized dividends (in dollars per share)	0.075
Quarterly Average Realized Price, Level 4 [Member]
Quarterly dividend per share (in dollars per share)	0.025
Annual dividend per share (in dollars per share)	0.10
Minimum annual component per share (in dollars per share)	0.015
Annualized dividends (in dollars per share)	0.115
Quarterly Average Realized Price, Level 5 [Member]
Quarterly dividend per share (in dollars per share)	0.035
Annual dividend per share (in dollars per share)	0.14
Minimum annual component per share (in dollars per share)	0.015
Annualized dividends (in dollars per share)	0.155
Quarterly Average Realized Price, Level 6 [Member]
Quarterly dividend per share (in dollars per share)	0.045
Annual dividend per share (in dollars per share)	0.18
Minimum annual component per share (in dollars per share)	0.015
Annualized dividends (in dollars per share)	0.195
Quarterly Average Realized Price, Level 7 [Member]
Quarterly dividend per share (in dollars per share)	0.055
Annual dividend per share (in dollars per share)	0.22
Minimum annual component per share (in dollars per share)	0.015
Annualized dividends (in dollars per share)	$ 0.235