Risk Concentrations (Narrative) (Details) $ in Thousands, T in Millions	12 Months Ended
Dec. 31, 2023 USD ($) T	Dec. 31, 2022 USD ($)
Concentration Risk [Line Items]
Trade accounts receivable	$ 273,522	$ 236,999
Tons of coal sold \| T	75.0
Percentage of tons sold under long term contract	75.00%
Long term contracts percentage of company revenue	46.00%
Long-term contracts, life term, minimum	1 year
Long-term contracts, life term, maximum	4 years
Electric utilities
Concentration Risk [Line Items]
Receivables	$ 67,200	$ 94,100
Percentage of total trade accounts receivable	25.00%	40.00%
Domestic and foreign steel producers
Concentration Risk [Line Items]
Trade accounts receivable	$ 206,300	$ 142,900
Trade receivables, percentage	75.00%	60.00%

Accounts receivables percentage of total trade

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- Definition

Goods sold during the year

+ References

No definition available.

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- Definition

The maximum life term of a long-term sales contract.

+ References

No definition available.

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- Definition

The minimum life term of a long-term sales contract.

+ References

No definition available.

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- Definition

Percentage of total company revenue

+ References

No definition available.

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- Definition

Percentage of accounts receivable net current.

+ References

No definition available.

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- Definition

Percentage of goods sold under long term contract

+ References

No definition available.

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- Definition

Amount, after allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481990/310-10-45-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481990/310-10-45-9

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 954
-SubTopic 310
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481027/954-310-50-2

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- Definition

The total amount due to the entity within one year of the balance sheet date (or one operating cycle, if longer) from outside sources, including trade accounts receivable, notes and loans receivable, as well as any other types of receivables, net of allowances established for the purpose of reducing such receivables to an amount that approximates their net realizable value.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 852
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481372/852-10-55-10

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