Fair Value Disclosure (Narrative) (Details) (USD $) In Millions, unless otherwise specified				9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Sep. 30, 2013 Reed Minerals	Aug. 31, 2012 Reed Minerals T
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Purchase price					$ 70.9
Liability for contingent consideration					1.6
Tons of coal sold from reserves covered in earn-out period for earn-out calculation					15,000,000
Earn-out payments (less than $0.1 million for nine months ended September 30, 2013)				0.1
Decrease in contingent consideration liability				2.4
Long-term debt excluding capital leases	161.8	166.8	204.1
Long-term Debt	$ 161.4	$ 166.0	$ 203.1