Joint Venture with Peabody Energy (Details) $ in Millions	3 Months Ended
Mar. 31, 2020 USD ($)
Implementation Agreement
Schedule of Equity Method Investments [Line Items]
Incurred expenses related to regulatory approval process	$ 3.7

A fee charged for services from professionals such as doctors, lawyers and accountants. The term is often expanded to include other professions, for example, pharmacists charging to maintain a medicinal profile of a client or customer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07.2(a),(b),(c),(d))
-URI http://asc.fasb.org/extlink&oid=120401555&loc=SL114874292-224272

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 220
-Section 45
-Paragraph 3
-Subparagraph (k)
-URI http://asc.fasb.org/extlink&oid=118262090&loc=SL114874205-224268

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