Note 8 - Common Stock Dividend Policy (Details)	3 Months Ended
	Mar. 31, 2016 $ / shares $ / item
Thirty Dollar [Member]
Quarterly average realized silver price per ounce | $ / item	30
Quarterly dividend per share (in dollars per share)	$ 0.01
Annualized dividend per share (in dollars per share)	$ 0.04
$35 [Member]
Quarterly average realized silver price per ounce | $ / item	35
Quarterly dividend per share (in dollars per share)	$ 0.02
Annualized dividend per share (in dollars per share)	$ 0.08
$40 [Member]
Quarterly average realized silver price per ounce | $ / item	40
Quarterly dividend per share (in dollars per share)	$ 0.03
Annualized dividend per share (in dollars per share)	$ 0.12
$45 [Member]
Quarterly average realized silver price per ounce | $ / item	45
Quarterly dividend per share (in dollars per share)	$ 0.04
Annualized dividend per share (in dollars per share)	$ 0.16
$50 [Member]
Quarterly average realized silver price per ounce | $ / item	50
Quarterly dividend per share (in dollars per share)	$ 0.05
Annualized dividend per share (in dollars per share)	$ 0.20