Derivatives - Net derivatives as reflected on the balance sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Derivatives, Fair Value [Line Items]
Net derivatives as classified in the balance sheet	$ 1,281	$ 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	$ 1,281	$ 2,707

Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 55
-Paragraph 13
-SubTopic 20
-Topic 210
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
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-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
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-Publisher FASB
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant