Note 8 - Stockholders' Equity - Common Stock Dividend Policy (Details) - USD ($)		1 Months Ended	9 Months Ended
	Sep. 01, 2020	Feb. 29, 2012	Sep. 30, 2020
Quarterly average realized silver price per ounce	$ 25	$ 30
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