Derivatives - Disclosure of fair Value of derivatives (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Derivative [Line Items]
Derivative Assets	$ 2,707	$ 6,104
Derivative Liabilities	0	(2,203)
Effect of counterparty netting in derivative assets		(1,890)
Effect of counterparty netting in derivative liabilities	0	1,890
Derivative Asset	2,707	$ 4,214
Derivative Asset, Statement of Financial Position [Extensible Enumeration]		Other Assets, Current
Derivative Liability	0	$ (313)
Derivative Liability, Statement of Financial Position [Extensible Enumeration]		Accrued Liabilities, Current
Net derivatives as classified in the balance sheets	2,707	$ 3,901
Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative Assets	2,707	6,104
Derivative Liabilities	0	(2,203)
Coal | Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative Assets	1,407	4,885
Derivative Liabilities	0	(2,203)
Heating oil - diesel purchases | Not Designated as Hedging Instrument
Derivative [Line Items]
Derivative Assets	1,300	$ 1,219
Derivative Liabilities	$ 0