Asset Impairment (Notes)	3 Months Ended
Mar. 31, 2017
Asset Impairment Charges [Abstract]
Asset Impairment Charges [Text Block]	Asset Impairment The Company's mining and exploration assets and mining-related investments may be adversely affected by numerous uncertain factors that may cause the Company to be unable to recover all or a portion of the carrying value of those assets. As a result of various unfavorable conditions, including but not limited to sustained trends of weakness in U.S. and international seaborne coal market pricing and certain asset-specific factors, the Company recognized aggregate impairment charges of $247.9 million, $1,277.8 million, and $154.4 million during the years ended December 31, 2016, 2015 and 2014, respectively. For additional information surrounding those charges, refer to Note 4. "Asset Impairment" to the consolidated financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2016. The Company generally does not view short-term declines subsequent to previous impairment assessments in thermal and metallurgical coal prices in the markets in which it sells its products as an indicator of impairment. However, the Company generally views a sustained trend (for example, over periods exceeding one year) of adverse coal market pricing or unfavorable changes thereto as a potential indicator of impairment. Because of the volatile and cyclical nature of U.S. and international seaborne coal markets, it is reasonably possible that prices in those market segments may decrease and/or fail to improve in the near term, which, absent sufficient mitigation such as an offsetting reduction in the Company's operating costs, may result in the need for future adjustments to the carrying value of the Company's long-lived mining assets and mining-related investments. During the three months ended March 31, 2017 and 2016, the Company recognized impairment charges of $30.5 million related to terminated coal lease contracts in the Midwestern United States, and $17.2 million to write down certain targeted divestiture assets in Queensland, Australia from their carrying value to their estimated fair value, respectively. The Company's assets whose recoverability and values are most sensitive to near-term pricing and other market factors include certain Australian metallurgical and thermal assets for which impairment charges were recorded in 2015, certain U.S. coal mines for which management's estimates for future cash flows from operations have declined, and other U.S. coal properties being leased to unrelated mining companies under royalty agreements. These assets had an aggregate carrying value of $1,367.6 million as of March 31, 2017. The Company conducted a review of those assets for recoverability as of March 31, 2017 and determined that no impairment charge was necessary as of that date. However, the carrying value of these assets will likely be adjusted downward in connection with emergence from the Chapter 11 Cases and the related fresh start reporting rules, mitigating the exposure to future impairment charges.

Asset Impairment

The Company's mining and exploration assets and mining-related investments may be adversely affected by numerous uncertain factors that may cause the Company to be unable to recover all or a portion of the carrying value of those assets. As a result of various unfavorable conditions, including but not limited to sustained trends of weakness in U.S. and international seaborne coal market pricing and certain asset-specific factors, the Company recognized aggregate impairment charges of $247.9 million, $1,277.8 million, and $154.4 million during the years ended December 31, 2016, 2015 and 2014, respectively. For additional information surrounding those charges, refer to Note 4. "Asset Impairment" to the consolidated financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2016.

The Company generally does not view short-term declines subsequent to previous impairment assessments in thermal and metallurgical coal prices in the markets in which it sells its products as an indicator of impairment. However, the Company generally views a sustained trend (for example, over periods exceeding one year) of adverse coal market pricing or unfavorable changes thereto as a potential indicator of impairment. Because of the volatile and cyclical nature of U.S. and international seaborne coal markets, it is reasonably possible that prices in those market segments may decrease and/or fail to improve in the near term, which, absent sufficient mitigation such as an offsetting reduction in the Company's operating costs, may result in the need for future adjustments to the carrying value of the Company's long-lived mining assets and mining-related investments.

During the three months ended March 31, 2017 and 2016, the Company recognized impairment charges of $30.5 million related to terminated coal lease contracts in the Midwestern United States, and $17.2 million to write down certain targeted divestiture assets in Queensland, Australia from their carrying value to their estimated fair value, respectively.

The Company's assets whose recoverability and values are most sensitive to near-term pricing and other market factors include certain Australian metallurgical and thermal assets for which impairment charges were recorded in 2015, certain U.S. coal mines for which management's estimates for future cash flows from operations have declined, and other U.S. coal properties being leased to unrelated mining companies under royalty agreements. These assets had an aggregate carrying value of $1,367.6 million as of March 31, 2017. The Company conducted a review of those assets for recoverability as of March 31, 2017 and determined that no impairment charge was necessary as of that date. However, the carrying value of these assets will likely be adjusted downward in connection with emergence from the Chapter 11 Cases and the related fresh start reporting rules, mitigating the exposure to future impairment charges.