Note 8. Shareholders' Equity (Detail) - Summary of Common Stock Dividends Declared (USD $)	Sep. 30, 2012
February 17, 2012 [Member]
Silver price linked compenent per share	$ 0.01
minimum annual component per share	$ 0.0025
Total dividend per share	$ 0.0125
Total dividend amount (in Dollars)	$ 3.6
May 8, 2012 [Member]
Silver price linked compenent per share	$ 0.02
minimum annual component per share	$ 0.0025
Total dividend per share	$ 0.0225
Total dividend amount (in Dollars)	6.4
August 7, 2012 [Member]
minimum annual component per share	$ 0.0025
Total dividend per share	$ 0.0025
Total dividend amount (in Dollars)	0.7
November 2, 2012 [Member]
Silver price linked compenent per share	$ 0.02
minimum annual component per share	$ 0.0025
Total dividend per share	$ 0.0225
Total dividend amount (in Dollars)	$ 6.4