Derivatives - Schedule of price risk derivatives (Details) - Coal purchases T in Thousands	9 Months Ended
Sep. 30, 2023 T
Derivative [Line Items]
Derivatives held (in tons)	7
2024
Derivative [Line Items]
Derivatives held (in tons)	7

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480237/815-40-50-5

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