Derivatives (Schedule of Price Risk Derivatives) (Details)	Mar. 31, 2013
Coal Sales [Member]
Derivative [Line Items]
Derivatives Held	10,439,000
Coal Purchases [Member]
Derivative [Line Items]
Derivatives Held	2,391,000
Year One [Member] | Coal Sales [Member]
Derivative [Line Items]
Derivatives Held	5,399,000
Year One [Member] | Coal Purchases [Member]
Derivative [Line Items]
Derivatives Held	1,131,000
Year Two [Member] | Coal Sales [Member]
Derivative [Line Items]
Derivatives Held	4,260,000
Year Two [Member] | Coal Purchases [Member]
Derivative [Line Items]
Derivatives Held	1,260,000
Year Three [Member] | Coal Sales [Member]
Derivative [Line Items]
Derivatives Held	780,000
Year Three [Member] | Coal Purchases [Member]
Derivative [Line Items]
Derivatives Held