Commitments and Contingent Liabilities (Details) - Uninsured Risk - USD ($) $ in Millions		12 Months Ended
Feb. 21, 2020	Dec. 31, 2013	Sep. 30, 2020	Dec. 31, 2019
Loss Contingencies [Line Items]
Accrual for black lung liability			$ 56.6	$ 55.1
Accrual for black lung liability, current			$ 4.6	$ 4.6
Collateral to secure black lung obligations	$ 40.4	$ 8.4

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Amount of loss contingency liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349

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Amount of loss contingency liability expected to be resolved within one year or the normal operating cycle, if longer.

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Amount of cash outflow reducing loss contingency liability.

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