Note 18. Subsequent Events (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Planned Capital Expenditures	$ 50.0
Loose Cementitous Material [Member]
Planned Capital Expenditures	10.0
Other Capital Projects [Member]
Planned Capital Expenditures	20.0
Shaft Improvements [Member]
Planned Capital Expenditures	20.0
Non-Capitalized Exenses [Member]
Planned Capital Expenditures	$ 17.5