Derivatives (Schedule of Price Risk Derivatives) (Details) T in Thousands	Sep. 30, 2016 T
Coal sales [Member]
Derivative [Line Items]
Derivatives Held	595
Coal purchases [Member]
Derivative [Line Items]
Derivatives Held	540
2016 [Member] | Coal sales [Member]
Derivative [Line Items]
Derivatives Held	55
2016 [Member] | Coal purchases [Member]
Derivative [Line Items]
Derivatives Held	60
2017 [Member] | Coal sales [Member]
Derivative [Line Items]
Derivatives Held	540
2017 [Member] | Coal purchases [Member]
Derivative [Line Items]
Derivatives Held	480