Property, Plant And Equipment (Narrative) (Details) $ in Thousands, T in Millions	1 Months Ended	3 Months Ended		9 Months Ended	12 Months Ended
	Aug. 31, 2015 USD ($) a	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Sep. 30, 2015 USD ($) T	Dec. 31, 2014 USD ($)
Property, Plant and Equipment [Line Items]
Loss on asset impairments		$ 2,333		$ 4,512
Non-current assets held for sale		15,699		15,699	$ 9,279
Non-current liabilities held for sale		6,823		$ 6,823	2,250
Deane Branch, Eastern Kentucky [Member]
Property, Plant and Equipment [Line Items]
Proven and probable coal reserves | T				39.3
Loss on asset impairments		2,300		$ 2,300
Mineral properties		2,000		2,000
Non-current assets held for sale		8,800		8,800
Non-current liabilities held for sale		$ 6,800		$ 6,800
Western Oklahoma [Member]
Property, Plant and Equipment [Line Items]
Loss on asset impairments			$ 2,200
Mineral properties			5,800
Property sold during period, net acreage | a	1,900
Proceeds from the sale of property	$ 5,700
Bevins Branch, Eastern Kentucky [Member]
Property, Plant and Equipment [Line Items]
Non-current assets held for sale			$ 2,300
Impairment charges					$ 8,300