Risk Concentrations (Narrative) (Details) $ in Thousands, T in Millions	12 Months Ended
Dec. 31, 2022 USD ($) T	Dec. 31, 2021 USD ($)
Concentration Risk [Line Items]
Trade accounts receivable	$ 236,999	$ 324,304
Tons of coal sold \| T	78.3
Percentage of tons sold under long term contract	68.00%
Long term contracts percentage of company revenue	36.00%
Long-term contracts, life term, minimum	1 year
Long-term contracts, life term, maximum	5 years
Electric utilities
Concentration Risk [Line Items]
Receivables	$ 94,100	$ 72,800
Percentage of total trade accounts receivable	40.00%	22.00%
Domestic and foreign steel producers
Concentration Risk [Line Items]
Trade accounts receivable	$ 142,900	$ 251,500
Trade receivables, percentage	60.00%	78.00%

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(5))
-URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section S99
-Paragraph 3
-Subparagraph (SX 210.6-06(3))
-URI https://asc.fasb.org/extlink&oid=120401414&loc=d3e604059-122996

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
-SubTopic 10
-Section 55
-Paragraph 10
-URI https://asc.fasb.org/extlink&oid=84165509&loc=d3e56426-112766

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant