Note 8 - Stockholders' Equity - Common Stock Dividend Policy (Details)	3 Months Ended
	Mar. 31, 2020 $ / shares
Quarterly Average Realized Price, Level 1 [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 2 [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 3 [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 4 [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 5 [Member]
Quarterly dividend per share (in dollars per share)	0.05
Annual dividend per share (in dollars per share)	$ 0.20