Basis of Presentation (Details) (USD $)	3 Months Ended		9 Months Ended			3 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Mar. 31, 2013	Jun. 30, 2013 Western Coal Corp Purchase price allocation adjustments
Basis of Presentation
Amount of the prior year fourth quarter impact of cash dividend declared and paid had reclassification been made from accumulated deficit to capital in excess of par value					$ 7,800,000
Amount of the prior year first quarter impact had reclassification been made from selling, general and administrative costs to cost of sales		5,700,000		19,100,000
Business acquisition
Depreciation and depletion	$ (82,986,000)	$ (82,560,000)	$ (232,496,000)	$ (223,512,000)		$ 8,400,000