Coal Workers' Pneumoconiosis and Workers' Compensation (Schedule of Expected Benefit Payments) (Details) $ in Thousands	Dec. 31, 2019 USD ($)
CWP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2020	$ 12,331
2021	12,013
2022	11,893
2023	11,545
2024	11,351
Year 2025-2029	57,446
Workers' Compensation
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2020	12,235
2021	12,427
2022	12,680
2023	12,741
2024	12,808
Year 2025-2029	66,260
Actuarial Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2020	10,286
2021	10,430
2022	10,633
2023	10,643
2024	10,657
Year 2025-2029	54,672
Other Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2020	1,949
2021	1,997
2022	2,047
2023	2,098
2024	2,151
Year 2025-2029	$ 11,588

Amount of benefits for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following latest fiscal year.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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