Commitments and Contingencies (Narrative) (Details) (USD $)	1 Months Ended						1 Months Ended
	Jul. 31, 2013	Sep. 30, 2014	Dec. 31, 2013	Aug. 25, 2011	May 02, 2011	Aug. 13, 2007	Feb. 01, 2011 Maximum [Member]	Feb. 01, 2011 Minimum [Member]	Aug. 25, 2011 past damages [Member]	Aug. 25, 2011 future damages [Member]
Purchase replacement coal, excess of						$ 100,000,000
Aggregate amount of past and future damages							377,000,000	228,000,000
Damages and interest awarded				104,100,000	104,100,000				13,800,000	90,300,000
Payments for Legal Settlements	15,600,000
Amount accrued		22,500,000	30,400,000
Amount accrued current portion		$ 10,300,000	$ 11,700,000