Concentrations of Credit Risk (Details) (Customer Concentration Risk [Member])	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Sales Revenue, Goods, Net [Member] | XCoal Energy and Resources [Member]
Concentration Risk [Line Items]
Concentration Risk, Customer	344617	495242	382843
Sales Revenue, Goods, Net [Member] | Duke Energy [Member]
Concentration Risk [Line Items]
Concentration Risk, Customer	394849	346424
Accounts Receivable [Member]
Concentration Risk [Line Items]
Concentration Risk, Customer	259817	332574
Accounts Receivable [Member] | Gas Customers [Member]
Concentration Risk [Line Items]
Concentration Risk, Customer	117985	71441
Accounts Receivable [Member] | All Other [Member]
Concentration Risk [Line Items]
Concentration Risk, Customer	4279	43199
Accounts Receivable [Member] | Coal Brokers and Distributors [Member]
Concentration Risk [Line Items]
Concentration Risk, Customer	41983	52233
Accounts Receivable [Member] | Steel and Coke Producers [Member]
Concentration Risk [Line Items]
Concentration Risk, Customer	10043	10963
Accounts Receivable [Member] | Steam Coal Utilities [Member]
Concentration Risk [Line Items]
Concentration Risk, Customer	85527	154738