Note 9 - Stockholders' Equity (Details) - Common Stock Dividends Declared by Our Board of Directors $ / shares in Units, $ in Millions	Dec. 31, 2015 USD ($) $ / shares
Declared February 25, 2013 [Member]
Dividends Payable [Line Items]
Silver-price-linked component per share	$ 0
Minimum annual component per share	0.0025
Special dividend per share	0.01
Total dividend per share	$ 0.0125
Total dividend amount (in Dollars) | $	$ 3.6
Declared May 10, 2013 [Member]
Dividends Payable [Line Items]
Silver-price-linked component per share	$ 0
Minimum annual component per share	0.0025
Special dividend per share	0
Total dividend per share	$ 0.0025
Total dividend amount (in Dollars) | $	$ 0.7
Declared August 8, 2013 [Member]
Dividends Payable [Line Items]
Silver-price-linked component per share	$ 0
Minimum annual component per share	0.0025
Special dividend per share	0
Total dividend per share	$ 0.0025
Total dividend amount (in Dollars) | $	$ 0.9
Declared November 5, 2013 [Member]
Dividends Payable [Line Items]
Silver-price-linked component per share	$ 0
Minimum annual component per share	0.0025
Special dividend per share	0
Total dividend per share	$ 0.0025
Total dividend amount (in Dollars) | $	$ 0.9
Declared February 21, 2014 [Member]
Dividends Payable [Line Items]
Silver-price-linked component per share	$ 0
Minimum annual component per share	0.0025
Special dividend per share	0
Total dividend per share	$ 0.0025
Total dividend amount (in Dollars) | $	$ 0.9
Declared May 5, 2014 [Member]
Dividends Payable [Line Items]
Silver-price-linked component per share	$ 0
Minimum annual component per share	0.0025
Special dividend per share	0
Total dividend per share	$ 0.0025
Total dividend amount (in Dollars) | $	$ 0.9
Declared July 31, 2014 [Member]
Dividends Payable [Line Items]
Silver-price-linked component per share	$ 0
Minimum annual component per share	0.0025
Special dividend per share	0
Total dividend per share	$ 0.0025
Total dividend amount (in Dollars) | $	$ 0.9
Declared November 5, 2014 [Member]
Dividends Payable [Line Items]
Silver-price-linked component per share	$ 0
Minimum annual component per share	0.0025
Special dividend per share	0
Total dividend per share	$ 0.0025
Total dividend amount (in Dollars) | $	$ 0.9
Declared February 17, 2015 [Member]
Dividends Payable [Line Items]
Silver-price-linked component per share	$ 0
Minimum annual component per share	0.0025
Special dividend per share	0
Total dividend per share	$ 0.0025
Total dividend amount (in Dollars) | $	$ 0.9
Declared May 6, 2015 [Member]
Dividends Payable [Line Items]
Silver-price-linked component per share	$ 0
Minimum annual component per share	0.0025
Special dividend per share	0
Total dividend per share	$ 0.0025
Total dividend amount (in Dollars) | $	$ 0.9
Declared August 6, 2015 [Member]
Dividends Payable [Line Items]
Silver-price-linked component per share	$ 0
Minimum annual component per share	0.0025
Special dividend per share	0
Total dividend per share	$ 0.0025
Total dividend amount (in Dollars) | $	$ 0.9
Declared November 3, 2015 [Member]
Dividends Payable [Line Items]
Silver-price-linked component per share	$ 0
Minimum annual component per share	0.0025
Special dividend per share	0
Total dividend per share	$ 0.0025
Total dividend amount (in Dollars) | $	$ 0.9
Declared February 20, 2016 [Member]
Dividends Payable [Line Items]
Silver-price-linked component per share	$ 0
Minimum annual component per share	0.0025
Special dividend per share	0
Total dividend per share	$ 0.0025
Total dividend amount (in Dollars) | $	$ 0.9