Derivatives (Schedule of Price Risk Derivatives) (Details) T in Thousands	12 Months Ended
	Dec. 31, 2019 T
Coal sales
Derivative [Line Items]
Derivatives Held	668
Coal purchases
Derivative [Line Items]
Derivatives Held	668
2019 | Coal sales
Derivative [Line Items]
Derivatives Held	668
2019 | Coal purchases
Derivative [Line Items]
Derivatives Held	668
2020 | Coal sales
Derivative [Line Items]
Derivatives Held	0
2020 | Coal purchases
Derivative [Line Items]
Derivatives Held	0