Derivatives (Schedule of Price Risk Derivatives) (Details) T in Thousands	Sep. 30, 2015 T
Coal sales [Member]
Derivative [Line Items]
Derivatives Held	1,485
Coal purchases [Member]
Derivative [Line Items]
Derivatives Held	936
Year One, Remainder [Member] | Coal sales [Member]
Derivative [Line Items]
Derivatives Held	1,205
Year One, Remainder [Member] | Coal purchases [Member]
Derivative [Line Items]
Derivatives Held	696
Year Two [Member] | Coal sales [Member]
Derivative [Line Items]
Derivatives Held	280
Year Two [Member] | Coal purchases [Member]
Derivative [Line Items]
Derivatives Held	240