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Management - Labor Relations Labor Relations (Details) | 12 Months Ended
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Dec. 31, 2016
Concentration Risk [Line Items] |
Entity Number of Employees | 6,700
Entity Number Of Hourly Employees | 5,100
Percentage of hourly employees represented by organized labor unions | 39.00%
Percentage Of Coal Production Generated By Hourly Employees Represented By Organized Labor Unions | 22.00%
Number of US Mines Represented by Unions | 1
United Mine Workers of America [Member] |
Concentration Risk [Line Items] |
Percentage of hourly employees represented by organized labor unions | 8.00%
Percentage Of Coal Production Generated By Hourly Employees | 4.00%
North Wambo UG Employees [Domain] |
Concentration Risk [Line Items] |
Percentage Of Coal Production Generated By Australian Hourly Employees Under Contract Negotiation | 10.00%
North Wambo UG Employees [Member] |
Concentration Risk [Line Items] |
Percentage Of Australian Hourly Employees Under Contract Negotiations | 8.00%
Metropolitan Employees [Member] |
Concentration Risk [Line Items] |
Percentage Of Australian Hourly Employees Under Contract Negotiations | 11.00%
Percentage Of Coal Production Generated By Australian Hourly Employees Under Contract Negotiation | 6.00%
Millenium 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 | 11.00%
Wilpinjong Employees [Member] |
Concentration Risk [Line Items] |
Percentage Of Australian Hourly Employees Under Contract Negotiations | 18.00%
Percentage Of Coal Production Generated By Australian Hourly Employees Under Contract Negotiation | 42.00%
Coppabella/Moorvale Employees [Member] |
Concentration Risk [Line Items] |
Percentage Of Australian Hourly Employees Under Contract Negotiations | 28.00%
Percentage Of Coal Production Generated By Australian Hourly Employees Under Contract Negotiation | 13.00%

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