Note 8. Shareholders’ Equity (Detail) - Potential Per Share Dividend Amounts (USD $)	Sep. 30, 2011
Thirty Dollars [Member] | Quarterly [Member]
Quarterly average realized silver price per ounce	$ 0.01
Thirty Dollars [Member] | Annual [Member]
Quarterly average realized silver price per ounce	$ 0.04
Thirty Five Dollars [Member] | Quarterly [Member]
Quarterly average realized silver price per ounce	$ 0.02
Thirty Five Dollars [Member] | Annual [Member]
Quarterly average realized silver price per ounce	$ 0.08
Forty Dollars [Member] | Quarterly [Member]
Quarterly average realized silver price per ounce	$ 0.03
Forty Dollars [Member] | Annual [Member]
Quarterly average realized silver price per ounce	$ 0.12
Forty Five Dollars [Member] | Quarterly [Member]
Quarterly average realized silver price per ounce	$ 0.04
Forty Five Dollars [Member] | Annual [Member]
Quarterly average realized silver price per ounce	$ 0.16
Fifty Dollars [Member] | Quarterly [Member]
Quarterly average realized silver price per ounce	$ 0.05
Fifty Dollars [Member] | Annual [Member]
Quarterly average realized silver price per ounce	$ 0.20
Fifty Five Dollars [Member] | Quarterly [Member]
Quarterly average realized silver price per ounce	$ 0.06
Fifty Five Dollars [Member] | Annual [Member]
Quarterly average realized silver price per ounce	$ 0.24
Sixty Dollars [Member] | Quarterly [Member]
Quarterly average realized silver price per ounce	$ 0.07
Sixty Dollars [Member] | Annual [Member]
Quarterly average realized silver price per ounce	$ 0.28