Equity Investments - Additional Information (Details) $ in Millions	Dec. 31, 2019 USD ($)
Fort Union [Member]
Schedule of Equity Method Investments [Line Items]
Equity investment difference between carrying and underlying value	$ (3.1)
Rendezvous [Member]
Schedule of Equity Method Investments [Line Items]
Equity investment difference between carrying and underlying value	32.4
White Cliffs [Member]
Schedule of Equity Method Investments [Line Items]
Equity investment difference between carrying and underlying value	$ (5.8)
White Cliffs [Member] \| Affiliates [Member]
Schedule of Equity Method Investments [Line Items]
Equity investment ownership percentage	0.40%
Whitethorn LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity investment difference between carrying and underlying value	$ (37.3)

Difference between amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

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- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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