Resource Management, Acquisitions and Other Commercial Events	12 Months Ended
Dec. 31, 2015
Resource Management, Acquisitions and Other Commercial Events [Abstract]
Resource Management, Acquisitions and Other Commercial Events	Resource Management, Acquisitions and Other Commercial Events Organizational Realignment From time to time, the Company initiates restructuring activities in connection with its repositioning efforts to appropriately align its cost structure or optimize its coal production relative to prevailing global coal industry conditions. Costs associated with restructuring actions can include early mine closures, voluntary and involuntary workforce reductions, office closures and other related activities. Costs associated with restructuring activities are recognized in the period incurred. In 2015, the Company has eliminated corporate and regional staff positions in the U.S. and implemented workforce reductions of employee and contractor positions at multiple mines in Australia. Included in the Company's consolidated statements of operations for the year ended December 31, 2015 were aggregate restructuring charges of $23.5 million, primarily comprised of cash severance costs. Of that amount, $3.0 million remained accrued as of December 31, 2015. Coal Supply Agreement During April 2014, the Company finalized pricing under a sales agreement for one of its Western U.S. Mining segment customers. As a result of that agreement, the Company recognized additional contract revenue and sales-related expenses totaling $33.5 million and $6.4 million, respectively, during the year ended December 31, 2014 and will continue to realize higher prices for coal supplied pursuant to that agreement. Divestitures The Company initiated a review of its asset portfolio during the second quarter of 2015. In connection with that review and related marketing and divestiture approval processes conducted during the period, certain assets were classified as held-for-sale. Subsequent to the related write-downs, these assets had an aggregate carrying value of approximately $125 million and were included in "Other current assets" in the Company's consolidated balance sheet as of December 31, 2015. The results of operations and cash flows of such assets were not material to the consolidated financial statements for the periods presented in this report. In January 2016, the Company entered into a definitive agreement to sell its 5.06 percent participation interest in the Prairie State Energy Campus to the Wabash Valley Power Association for approximately $57 million, subject to certain customary closing adjustments, and satisfaction of closing condition and expiration of certain purchase rights, with the closing expected to occur in the second quarter of 2016. In November 2015, the Company entered into a definitive agreement to sell its El Segundo and Lee Ranch mines in New Mexico and its Twentymile Mine in Colorado to Bowie Resource Partners, LLC in exchange for cash proceeds of $358 million and the assumption of approximately $105 million in related liabilities. The transaction is scheduled to be completed during the first quarter of 2016. The mines were not classified as discontinued operations in the accompanying consolidated financial statements due to the level of uncertainty associated with completing the transaction at December 31, 2015. In January 2014, the Company sold a non-strategic exploration tenement asset in Australia in exchange for cash proceeds of $62.6 million. The Company had previously recorded an impairment charge in December 2013 to write down the carrying value of that asset to its fair value as discussed in Note 2. "Asset Impairment." Accordingly, there was no gain or loss recognized on the disposal during the year ended December 31, 2015. In December 2014, the Company sold non-strategic coal reserves located in Kentucky in exchange for cash proceeds of $29.6 million. The company recognized a gain on sale of $13.6 million related to the transaction, which was classified in "Net gain on disposal or exchange of assets" in the consolidated statement of operations for the year ended December 31, 2014. Joint Venture In 2014, the Company agreed to establish an unincorporated joint venture project with Glencore plc (Glencore), in which each party will hold a 50% interest, to combine the existing operations of the Company's Wambo Open-Cut Mine in Australia with the adjacent coal reserves of Glencore's United Mine. The Company expects the project to result in several operation synergies, including improved mining productivity, lower per-unit operating costs and an extended mine life. The joint venture operations are expected to commence in 2017, subject to substantive contingencies, including the requisite regulatory and permitting approvals. At such time as those contingencies have been resolved or are no longer considered to be substantive, the Company will account for its beneficial interest in the combined operations at fair value.

Resource Management, Acquisitions and Other Commercial Events

Organizational Realignment

From time to time, the Company initiates restructuring activities in connection with its repositioning efforts to appropriately align its cost structure or optimize its coal production relative to prevailing global coal industry conditions. Costs associated with restructuring actions can include early mine closures, voluntary and involuntary workforce reductions, office closures and other related activities. Costs associated with restructuring activities are recognized in the period incurred.

In 2015, the Company has eliminated corporate and regional staff positions in the U.S. and implemented workforce reductions of employee and contractor positions at multiple mines in Australia. Included in the Company's consolidated statements of operations for the year ended December 31, 2015 were aggregate restructuring charges of $23.5 million, primarily comprised of cash severance costs. Of that amount, $3.0 million remained accrued as of December 31, 2015.

Coal Supply Agreement

During April 2014, the Company finalized pricing under a sales agreement for one of its Western U.S. Mining segment customers. As a result of that agreement, the Company recognized additional contract revenue and sales-related expenses totaling $33.5 million and $6.4 million, respectively, during the year ended December 31, 2014 and will continue to realize higher prices for coal supplied pursuant to that agreement.

Divestitures

The Company initiated a review of its asset portfolio during the second quarter of 2015. In connection with that review and related marketing and divestiture approval processes conducted during the period, certain assets were classified as held-for-sale. Subsequent to the related write-downs, these assets had an aggregate carrying value of approximately $125 million and were included in "Other current assets" in the Company's consolidated balance sheet as of December 31, 2015. The results of operations and cash flows of such assets were not material to the consolidated financial statements for the periods presented in this report.

In January 2016, the Company entered into a definitive agreement to sell its 5.06 percent participation interest in the Prairie State Energy Campus to the Wabash Valley Power Association for approximately $57 million, subject to certain customary closing adjustments, and satisfaction of closing condition and expiration of certain purchase rights, with the closing expected to occur in the second quarter of 2016.

In November 2015, the Company entered into a definitive agreement to sell its El Segundo and Lee Ranch mines in New Mexico and its Twentymile Mine in Colorado to Bowie Resource Partners, LLC in exchange for cash proceeds of $358 million and the assumption of approximately $105 million in related liabilities. The transaction is scheduled to be completed during the first quarter of 2016. The mines were not classified as discontinued operations in the accompanying consolidated financial statements due to the level of uncertainty associated with completing the transaction at December 31, 2015.

In January 2014, the Company sold a non-strategic exploration tenement asset in Australia in exchange for cash proceeds of $62.6 million. The Company had previously recorded an impairment charge in December 2013 to write down the carrying value of that asset to its fair value as discussed in Note 2. "Asset Impairment." Accordingly, there was no gain or loss recognized on the disposal during the year ended December 31, 2015.

In December 2014, the Company sold non-strategic coal reserves located in Kentucky in exchange for cash proceeds of $29.6 million. The company recognized a gain on sale of $13.6 million related to the transaction, which was classified in "Net gain on disposal or exchange of assets" in the consolidated statement of operations for the year ended December 31, 2014.

Joint Venture

In 2014, the Company agreed to establish an unincorporated joint venture project with Glencore plc (Glencore), in which each party will hold a 50% interest, to combine the existing operations of the Company's Wambo Open-Cut Mine in Australia with the adjacent coal reserves of Glencore's United Mine. The Company expects the project to result in several operation synergies, including improved mining productivity, lower per-unit operating costs and an extended mine life. The joint venture operations are expected to commence in 2017, subject to substantive contingencies, including the requisite regulatory and permitting approvals. At such time as those contingencies have been resolved or are no longer considered to be substantive, the Company will account for its beneficial interest in the combined operations at fair value.