Note 10 - Stockholders' Equity - Common Stock Dividend Policy (Details)	12 Months Ended
	Dec. 31, 2020 $ / shares
Quarterly Average Realized Price, Level 1 [Member]
Quarterly dividend per share (in dollars per share)	$ 0.005
Annual dividend per share (in dollars per share)	0.02
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
Quarterly Average Realized Price, Level 3 [Member]
Quarterly dividend per share (in dollars per share)	0.02
Annual dividend per share (in dollars per share)	0.08
Quarterly Average Realized Price, Level 4 [Member]
Quarterly dividend per share (in dollars per share)	0.03
Annual dividend per share (in dollars per share)	0.12
Quarterly Average Realized Price, Level 5 [Member]
Quarterly dividend per share (in dollars per share)	0.04
Annual dividend per share (in dollars per share)	0.16
Quarterly Average Realized Price, Level 6 [Member]
Quarterly dividend per share (in dollars per share)	0.05
Annual dividend per share (in dollars per share)	0.20
Quarterly Average Realized Price, Level 7 [Member]
Quarterly dividend per share (in dollars per share)	0.06
Annual dividend per share (in dollars per share)	0.24
Quarterly Average Realized Price, Level 8 [Member]
Quarterly dividend per share (in dollars per share)	0.07
Annual dividend per share (in dollars per share)	$ 0.28