Coal Workers' Pneumoconiosis and Workers' Compensation (Schedule of Expected Benefit Payments) (Details) $ in Thousands	Dec. 31, 2018 USD ($)
CWP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2019	$ 12,187
2020	10,319
2021	9,753
2022	9,528
2023	9,633
Year 2024-2028	52,265
Workers' Compensation
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2019	13,987
2020	14,007
2021	13,800
2022	13,874
2023	13,766
Year 2024-2028	70,429
Actuarial Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2019	11,244
2020	11,196
2021	10,918
2022	10,920
2023	10,738
Year 2024-2028	54,117
Other Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2019	2,743
2020	2,811
2021	2,882
2022	2,954
2023	3,028
Year 2024-2028	$ 16,312

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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-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (f)
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