Property, Plant And Equipment (Depreciation, Depletion And Amortization) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Property, Plant and Equipment [Line Items]
Depreciation, depletion and amortization	$ 10,579	$ 9,755	$ 20,790	$ 20,847
Mining And Other Equipment And Related Facilities [Member]
Property, Plant and Equipment [Line Items]
Depreciation, depletion and amortization	7,901	7,700	16,037	16,464
Coal Properties And Oil And Natural Gas Properties [Member]
Property, Plant and Equipment [Line Items]
Depreciation, depletion and amortization	2,012	1,375	3,391	2,921
Mine Development Costs [Member]
Property, Plant and Equipment [Line Items]
Depreciation, depletion and amortization	617	512	1,287	1,124
Intangible Assets [Member]
Property, Plant and Equipment [Line Items]
Depreciation, depletion and amortization	20	20	41	41
Asset Retirement Costs [Member]
Property, Plant and Equipment [Line Items]
Depreciation, depletion and amortization	$ 29	$ 148	$ 34	$ 297