Subsequent Events	3 Months Ended
Mar. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events New Inventory Facility On April 27, 2017, the Company and certain subsidiaries of Arch Coal entered into a new senior secured inventory-based revolving credit facility in an aggregate principal amount of $40 million (the “New Inventory Facility”) with Regions Bank (“Regions”) as administrative agent and collateral agent (in such capacities, the “Agent”), as lender and swingline lender (in such capacities, the “Lender”) and as letter of credit issuer. Availability under the New Inventory Facility is subject to a borrowing base consisting of (i) 85% of the net orderly liquidation value of eligible coal inventory, (ii) the lesser of (x) 85% of the net orderly liquidation value of eligible parts and supplies inventory and (y) 35% of the amount determined pursuant to clause (i), and (iii) 100% of Arch Coal’s Eligible Cash (defined in the New Inventory Facility), subject to reduction for reserves imposed by Regions. The commitments under the New Inventory Facility will terminate on the date that is the earliest to occur of (i) the third anniversary of the Inventory Facility Closing Date, (ii) the date, if any, that is 364 days following the first day that Liquidity (defined in the New Inventory Facility and consistent with the definition in the Extended Securitization Facility (as defined below)) is less than $250 million for a period of 60 consecutive days and (iii) the date, if any, that is 60 days following the maturity, termination or repayment in full of the Extended Securitization Facility. Revolving loan borrowings under the New Inventory Facility bear interest at a per annum rate equal to, at the option of Arch Coal, either at the base rate or the London interbank offered rate plus, in each case, a margin ranging from 2.25% to 2.50% (in the case of LIBOR loans) and 1.25% to 1.50% (in the case of base rate loans) determined using a Liquidity-based grid. Letters of credit under the New Inventory Facility are subject to a fee in an amount equal to the applicable margin for LIBOR loans, plus customary fronting and issuance fees. All existing and future direct and indirect domestic subsidiaries of Arch Coal, subject to customary exceptions, will either constitute co-borrowers under or guarantors of the New Inventory Facility (collectively with Arch Coal, the “Loan Parties”). The New Inventory Facility is secured by first priority security interests in the ABL Priority Collateral (defined in the New Inventory Facility) of the Loan Parties and second priority security interests in substantially all other assets of the Loan Parties, subject to customary exceptions (including an exception for the collateral that secures the Extended Securitization Facility). Arch Coal has the right to prepay borrowings under the New Inventory Facility at any time and from time to time in whole or in part without premium or penalty, upon written notice, except that any prepayment of such borrowings that bear interest at the LIBOR rate other than at the end of the applicable interest periods therefor shall be made with reimbursement for any funding losses and redeployment costs of the Lender resulting therefrom. The New Inventory Facility is subject to certain usual and customary mandatory prepayment events, including non-ordinary course asset sales or dispositions, subject to customary thresholds, exceptions (including exceptions for required prepayments under Arch Coal’s term loan facility) and reinvestment rights. The New Inventory Facility contains certain customary affirmative and negative covenants; events of default, subject to customary thresholds and exceptions; and representations, including certain cash management and reporting requirements that are customary for asset-based credit facilities. The New Inventory Facility also includes a requirement to maintain Liquidity equal to or exceeding $175 million at all times. Securitization Facility On April 27, 2017, the Company extended and amended its existing trade accounts receivable securitization facility provided to Arch Receivable Company, LLC, a special-purpose entity that is a wholly owned subsidiary of Arch Coal (“Arch Receivable”) (the “Extended Securitization Facility”), which supports the issuance of letters of credit and requests for cash advances. The amendment to the Extended Securitization Facility decreases the borrowing capacity from $200 million to $160 million and extends the maturity date to the date that is three years after the Securitization Facility Closing Date. Pursuant to the Extended Securitization Facility, Arch Receivable also agreed to a revised schedule of fees payable to the administrator and the providers of the Extended Securitization Facility. The Extended Securitization Facility will terminate at the earliest of (i) three years from the Securitization Facility Closing Date, (ii) if the Liquidity (defined in the Extended Securitization Facility and consistent with the definition in the New Inventory Facility) is less than $175 million for a period of 60 consecutive days, the date that is the 364th day after the first day of such 60 consecutive day period and (iii) the occurrence of certain predefined events substantially consistent with the existing transaction documents. Under the Extended Securitization Facility, Arch Receivable, Arch Coal and certain of Arch Coal’s subsidiaries party to the Extended Securitization Facility have granted to the administrator of the Extended Securitization Facility a first priority security interest in eligible trade accounts receivable generated by such parties from the sale of coal and all proceeds thereof. Share Repurchase and Common Stock Dividend On April 27, 2017, the board of directors of Arch Coal authorized a new share repurchase program for up to $300 million of its common stock, effective April 27, 2017. The timing of any purchases, and the ultimate number of shares to be purchased, will depend on market conditions. The shares will be acquired in the open market or through private transactions in accordance with Securities and Exchange Commission requirements. The Company had 25,021,079 common shares outstanding as of April 27, 2017. The purchases under the new share repurchase program may be made in the open market or through privately negotiated transactions from time to time and in accordance with applicable laws, rules and regulations. Repurchases may also be made pursuant to a Rule 10b5-1 plan, which, if adopted by Company, would permit shares to be repurchased in accordance with pre-determined criteria when the Company might otherwise be prohibited from doing so under insider trading laws or because of self-imposed trading blackout periods. The share repurchase program may be amended, suspended or discontinued at any time and does not commit the Company to repurchase shares of its common stock. The actual number and value of the shares to be purchased will depend on the performance of the Company’s stock price and other market conditions. On April 27, 2017, the board of directors also authorized a new quarterly common stock cash dividend of $0.35 per share. The dividend will be paid on June 15, 2017 to stockholders of record on May 31, 2017.

Subsequent Events

New Inventory Facility

On April 27, 2017, the Company and certain subsidiaries of Arch Coal entered into a new senior secured inventory-based revolving credit facility in an aggregate principal amount of $40 million (the “New Inventory Facility”) with Regions Bank (“Regions”) as administrative agent and collateral agent (in such capacities, the “Agent”), as lender and swingline lender (in such capacities, the “Lender”) and as letter of credit issuer. Availability under the New Inventory Facility is subject to a borrowing base consisting of (i) 85% of the net orderly liquidation value of eligible coal inventory, (ii) the lesser of (x) 85% of the net orderly liquidation value of eligible parts and supplies inventory and (y) 35% of the amount determined pursuant to clause (i), and (iii) 100% of Arch Coal’s Eligible Cash (defined in the New Inventory Facility), subject to reduction for reserves imposed by Regions.

The commitments under the New Inventory Facility will terminate on the date that is the earliest to occur of (i) the third anniversary of the Inventory Facility Closing Date, (ii) the date, if any, that is 364 days following the first day that Liquidity (defined in the New Inventory Facility and consistent with the definition in the Extended Securitization Facility (as defined below)) is less than $250 million for a period of 60 consecutive days and (iii) the date, if any, that is 60 days following the maturity, termination or repayment in full of the Extended Securitization Facility.

Revolving loan borrowings under the New Inventory Facility bear interest at a per annum rate equal to, at the option of Arch Coal, either at the base rate or the London interbank offered rate plus, in each case, a margin ranging from 2.25% to 2.50% (in the case of LIBOR loans) and 1.25% to 1.50% (in the case of base rate loans) determined using a Liquidity-based grid. Letters of credit under the New Inventory Facility are subject to a fee in an amount equal to the applicable margin for LIBOR loans, plus customary fronting and issuance fees.

All existing and future direct and indirect domestic subsidiaries of Arch Coal, subject to customary exceptions, will either constitute co-borrowers under or guarantors of the New Inventory Facility (collectively with Arch Coal, the “Loan Parties”). The New Inventory Facility is secured by first priority security interests in the ABL Priority Collateral (defined in the New Inventory Facility) of the Loan Parties and second priority security interests in substantially all other assets of the Loan Parties, subject to customary exceptions (including an exception for the collateral that secures the Extended Securitization Facility).

Arch Coal has the right to prepay borrowings under the New Inventory Facility at any time and from time to time in whole or in part without premium or penalty, upon written notice, except that any prepayment of such borrowings that bear interest at the LIBOR rate other than at the end of the applicable interest periods therefor shall be made with reimbursement for any funding losses and redeployment costs of the Lender resulting therefrom.

The New Inventory Facility is subject to certain usual and customary mandatory prepayment events, including non-ordinary course asset sales or dispositions, subject to customary thresholds, exceptions (including exceptions for required prepayments under Arch Coal’s term loan facility) and reinvestment rights.

The New Inventory Facility contains certain customary affirmative and negative covenants; events of default, subject to customary thresholds and exceptions; and representations, including certain cash management and reporting requirements that are customary for asset-based credit facilities. The New Inventory Facility also includes a requirement to maintain Liquidity equal to or exceeding $175 million at all times.

Securitization Facility

On April 27, 2017, the Company extended and amended its existing trade accounts receivable securitization facility provided to Arch Receivable Company, LLC, a special-purpose entity that is a wholly owned subsidiary of Arch Coal (“Arch Receivable”) (the “Extended Securitization Facility”), which supports the issuance of letters of credit and requests for cash advances. The amendment to the Extended Securitization Facility decreases the borrowing capacity from $200 million to $160 million and extends the maturity date to the date that is three years after the Securitization Facility Closing Date. Pursuant to the Extended Securitization Facility, Arch Receivable also agreed to a revised schedule of fees payable to the administrator and the providers of the Extended Securitization Facility.

The Extended Securitization Facility will terminate at the earliest of (i) three years from the Securitization Facility Closing Date, (ii) if the Liquidity (defined in the Extended Securitization Facility and consistent with the definition in the New Inventory Facility) is less than $175 million for a period of 60 consecutive days, the date that is the 364th day after the first day of such 60 consecutive day period and (iii) the occurrence of certain predefined events substantially consistent with the existing transaction documents. Under the Extended Securitization Facility, Arch Receivable, Arch Coal and certain of Arch Coal’s subsidiaries party to the Extended Securitization Facility have granted to the administrator of the Extended Securitization Facility a first priority security interest in eligible trade accounts receivable generated by such parties from the sale of coal and all proceeds thereof.

Share Repurchase and Common Stock Dividend

On April 27, 2017, the board of directors of Arch Coal authorized a new share repurchase program for up to $300 million of its common stock, effective April 27, 2017. The timing of any purchases, and the ultimate number of shares to be purchased, will depend on market conditions. The shares will be acquired in the open market or through private transactions in accordance with Securities and Exchange Commission requirements. The Company had 25,021,079 common shares outstanding as of April 27, 2017.

The purchases under the new share repurchase program may be made in the open market or through privately negotiated transactions from time to time and in accordance with applicable laws, rules and regulations. Repurchases may also be made pursuant to a Rule 10b5-1 plan, which, if adopted by Company, would permit shares to be repurchased in accordance with pre-determined criteria when the Company might otherwise be prohibited from doing so under insider trading laws or because of self-imposed trading blackout periods. The share repurchase program may be amended, suspended or discontinued at any time and does not commit the Company to repurchase shares of its common stock. The actual number and value of the shares to be purchased will depend on the performance of the Company’s stock price and other market conditions.

On April 27, 2017, the board of directors also authorized a new quarterly common stock cash dividend of $0.35 per share. The dividend will be paid on June 15, 2017 to stockholders of record on May 31, 2017.