Property, Plant And Equipment (Property, Plant And Equipment By Major Classification) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Total	$ 650,628	$ 663,662
Less accumulated depreciation, depletion and amortization	(288,328)	(280,225)
Net property, plant and equipment	362,300	383,437
Land And Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Total	18,799	18,845
Mining And Other Equipment And Related Facilities [Member]
Property, Plant and Equipment [Line Items]
Total	333,481	336,951
Mine Development Costs [Member]
Property, Plant and Equipment [Line Items]
Total	76,285	79,536
Coal Properties [Member]
Property, Plant and Equipment [Line Items]
Total	219,018	215,325
Oil And Natural Gas Properties [Member]
Property, Plant and Equipment [Line Items]
Total		8,093
Construction Work In Process [Member]
Property, Plant and Equipment [Line Items]
Total	$ 3,045	$ 4,912
Minimum [Member] | Mining And Other Equipment And Related Facilities [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	2 years
Minimum [Member] | Mine Development Costs [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	1 year
Minimum [Member] | Coal Properties [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	1 year
Maximum [Member] | Mining And Other Equipment And Related Facilities [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	20 years
Maximum [Member] | Mine Development Costs [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	15 years
Maximum [Member] | Coal Properties [Member]
Property, Plant and Equipment [Line Items]
Useful Lives	15 years