Derivative Instruments (Derivative For Risk Management Purposes) (Details)	Dec. 31, 2011
Coal Purchases [Member] | One Year From Balance Sheet Date [Member]
Derivative [Line Items]
Quantities under derivative contracts, tons	254,000
Coal Purchases [Member] | More Than One And Within Two Years From Balance Sheet Date [Member]
Derivative [Line Items]
Quantities under derivative contracts, tons
Coal Purchases [Member] | More Than Two And Within Three Years From Balance Sheet Date [Member]
Derivative [Line Items]
Quantities under derivative contracts, tons
Coal Purchases [Member] | More Than Three And Within Four Years From Balance Sheet Date [Member]
Derivative [Line Items]
Quantities under derivative contracts, tons
Coal Sales [Member] | One Year From Balance Sheet Date [Member]
Derivative [Line Items]
Quantities under derivative contracts, tons	2,416,000
Coal Sales [Member] | More Than One And Within Two Years From Balance Sheet Date [Member]
Derivative [Line Items]
Quantities under derivative contracts, tons	1,117,000
Coal Sales [Member] | More Than Two And Within Three Years From Balance Sheet Date [Member]
Derivative [Line Items]
Quantities under derivative contracts, tons	1,440,000
Coal Sales [Member] | More Than Three And Within Four Years From Balance Sheet Date [Member]
Derivative [Line Items]
Quantities under derivative contracts, tons	720,000