Derivatives - Net derivatives as reflected on the balance sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Derivatives, Fair Value [Line Items]
Net derivatives as classified in the balance sheet	$ 833	$ 2,707
Other current assets
Derivatives, Fair Value [Line Items]
Current asset representing cash collateral posted	600	0
Heating oil and coal | Other current assets
Derivatives, Fair Value [Line Items]
Net derivatives as classified in the balance sheet	998	$ 2,707
Coal Contract | Accrued expenses and other current liabilities
Derivatives, Fair Value [Line Items]
Net derivatives as classified in the balance sheet	$ (165)