Note 4. Commitments and Contingencies (Detail) (USD $)	1 Months Ended							9 Months Ended	12 Months Ended					4 Months Ended	9 Months Ended		9 Months Ended	21 Months Ended	33 Months Ended	43 Months Ended
	Oct. 31, 2011	Jun. 30, 2011	Apr. 30, 2011	Jan. 31, 2010	Dec. 31, 2009	Apr. 30, 2009	Sep. 30, 2003	Sep. 30, 2011	Dec. 31, 2007	Sep. 30, 2012	Feb. 01, 2010	Sep. 30, 2002	Sep. 30, 2011 Greens Creek [Member]	Sep. 30, 2011 Greens Creek [Member]	Sep. 30, 2011 Greens Creek [Member]	Sep. 30, 2011 Lucky Friday [Member]	Sep. 30, 2011 Lucky Friday [Member]	Oct. 08, 2012 Accrual For Basin Claims Cash [Member]	Oct. 08, 2013 Accrual For Basin Claims Cash [Member]	Aug. 01, 2014 Accrual For Basin Claims Proceeds From Warrants [Member]	Aug. 01, 2014 Warrants Minimum Exercise Price [Member]	Aug. 01, 2014 Warrants Minimum Exercise Price [Member]
SuretyBonds	$ 96,400,000
Future Clean Up Costs											1,300,000,000	359,000,000
AllocatedShareOfLiability							31.00%
Claims For Natural Resource Damages, Lower Range							2,000,000,000
Claims For Natural Resource Damages, Upper Range							3,400,000,000
Proceeds from (Repayments of) Other Debt					482,000,000
PaymentsUnderConsentDecree	168
Payments for Legal Settlements																		25,000,000	15,000,000	56,400,000
Investment Warrants, Exercise Price (in Dollars per share)																					$ 2.45	$ 2.50
Superfund Rate								0.69%		0.74%
Other Accrued Liabilities, Noncurrent										262.3
Proceeds from Insurance Settlement, Operating Activities									7,200,000
Maximum Environmental Remediation Obligation								2.5
AdministrativePenalty						177,500
IncurredResponseCosts				91,000,000
EstimatedFutureResponseCost		100,000,000		72,000,000
ContributionAndCostRecovery			9,000,000
EstimatedResponseCosts		4,500,000
Purchase Commitment, Remaining Minimum Amount Committed								1,200,000
Noncapital Costs														400,000	0.3		0.4
Accounts Payable, Other													8.2			1.6
ApproximateCapitalLeaseObligationIncludingInterest								7,800,000
Letters of Credit Outstanding, Amount								600,000
Annual Maintenance Fee	$ 0.6