Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Name:	us-gaap_GoodwillImpairmentLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Basis of Presentation and Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Summary Of Significant Accounting Policies [Line Items]
Goodwill impairment		$ 0.0	$ 0.0	$ 0.0	$ 80.3
Loss on long-lived assets, net		$ 18.5	$ 21.3	19.6	26.1
Powder River Basin [Member]
Summary Of Significant Accounting Policies [Line Items]
Goodwill impairment					$ 80.3
Marcellus
Summary Of Significant Accounting Policies [Line Items]
Loss on long-lived assets, net				$ 19.0
Fayetteville
Summary Of Significant Accounting Policies [Line Items]
Gain (Loss) on Disposition of Assets	$ 19.9