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Management - Labor Relations Labor Relations (Details) | 3 Months Ended | 9 Months Ended
--- | --- | ---
Apr. 01, 2017 | Dec. 31, 2017
Concentration Risk [Line Items] |  |
Entity Number of Employees |  | 7,100
Entity Number Of Hourly Employees |  | 5,500
Percentage of hourly employees represented by organized labor unions |  | 38.00%
Percentage Of Coal Production Generated By Hourly Employees Represented By Organized Labor Unions | 20.00% |
Number of US Mines Represented by Unions |  | 1
Successor | United Mine Workers of America [Member] |  |
Concentration Risk [Line Items] |  |
Percentage of hourly employees represented by organized labor unions |  | 7.00%
Percentage Of Coal Production Generated By Hourly Employees | 4.00% |
Successor | North Wambo UG Employees [Member] |  |
Concentration Risk [Line Items] |  |
Percentage Of Australian Hourly Employees Under Contract Negotiations |  | 20.00%
Percentage Of Coal Production Generated By Australian Hourly Employees Under Contract Negotiation | 19.00% |
Successor | North Goonyella UG Employees [Member] |  |
Concentration Risk [Line Items] |  |
Percentage Of Australian Hourly Employees Under Contract Negotiations |  | 7.00%
Percentage Of Coal Production Generated By Australian Hourly Employees Under Contract Negotiation |  | 11.00%
Successor | Metropolitan Employees [Member] |  |
Concentration Risk [Line Items] |  |
Percentage Of Australian Hourly Employees Under Contract Negotiations |  | 12.00%
Percentage Of Coal Production Generated By Australian Hourly Employees Under Contract Negotiation |  | 3.00%
Successor | Coppabella/Moorvale Employees [Member] |  |
Concentration Risk [Line Items] |  |
Percentage Of Australian Hourly Employees Under Contract Negotiations |  | 16.00%
Percentage Of Coal Production Generated By Australian Hourly Employees Under Contract Negotiation | 9.00% |
Successor | Millenium Employees [Member] |  |
Concentration Risk [Line Items] |  |
Percentage Of Australian Hourly Employees Under Contract Negotiations |  | 15.00%
Percentage Of Coal Production Generated By Australian Hourly Employees Under Contract Negotiation |  | 10.00%
Successor | Wilpinjong Employees [Member] |  |
Concentration Risk [Line Items] |  |
Percentage Of Australian Hourly Employees Under Contract Negotiations |  | 21.00%
Percentage Of Coal Production Generated By Australian Hourly Employees Under Contract Negotiation |  | 42.00%

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