Mineral Rights, Net Schedule of Impairment Expense (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Asset impairments	$ 135,885	$ 148,214	$ 18,280
Carrying Value	$ 820,170	$ 1,048,389
Discount Rate	15.00%	15.00%	11.00%
Coal Mineral Rights
Property, Plant and Equipment [Line Items]
Asset impairments	$ 114,302	$ 125,806	$ 5,259
Carrying Value	785,623	981,352
Fair value of impaired assets		7,200
Aggregates properties
Property, Plant and Equipment [Line Items]
Asset impairments	21,583	103	13,021
Carrying Value	9,039	41,486
Fair value of impaired assets			2,300
Mining Properties and Mineral Rights
Property, Plant and Equipment [Line Items]
Asset impairments	$ 135,885	125,909	18,280
Fully Impaired \| Coal Mineral Rights
Property, Plant and Equipment [Line Items]
Asset impairments		36,000	$ 5,000
Partially Impaired \| Coal Mineral Rights
Property, Plant and Equipment [Line Items]
Asset impairments		89,800
Coal Mineral Rights \| Coal Mineral Rights
Property, Plant and Equipment [Line Items]
Carrying Value		$ 97,000

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- Definition

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Carrying amount at the balance sheet date of mineral properties, gross of adjustments.

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- Definition

Fair value portion of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

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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.

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