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Equity Method Investments - Textuals (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 9 Months Ended |
--- | --- | --- | --- | ---
Apr. 01, 2017 | Sep. 30, 2017 | Sep. 30, 2018 | Dec. 31, 2017
Successor |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Equity method investments and financing receivables |  |  | $ 66.4 | $ 82.1
Successor | Middlemount Mine |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Equity method investment, ownership percentage |  |  | 50.00% |
Successor | Financing Receivable | Middlemount Mine |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Financing receivable, cash received from equity Interest |  | $ 35.2 | $ 81.1 |
Predecessor | Financing Receivable | Middlemount Mine |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Financing receivable, cash received from equity Interest | $ 31.1 |  |  |

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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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571 + Details
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