Basis of Presentation (Policies)	6 Months Ended
Jun. 30, 2020
Basis of Presentation
Basis of Presentation	The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States for interim financial reporting and U.S. Securities and Exchange Commission regulations. In the opinion of management, all adjustments, consisting of normal, recurring accruals considered necessary for a fair presentation, have been included. Results of operations for the three and six months ended June 30, 2020 are not necessarily indicative of results to be expected for the year ending December 31, 2020. These financial statements should be read in conjunction with the audited financial statements and related notes as of and for the year ended December 31, 2019 included in the Company’s Annual Report on Form 10-K filed with the U.S. Securities and Exchange Commission. Effective May 15, 2020, Arch Coal, Inc. announced that its name changed to Arch Resources, Inc.
Recently Adopted Accounting Guidance	Recently Adopted Accounting Guidance In June 2016, the FASB issued ASU 2016-13, “Financial Instruments-Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments,” and also issued subsequent amendments to the initial guidance under ASU 2018-19, ASU 2019-04 and ASU 2019-05. The standard modifies the measurement approach for credit losses on financial instruments, including trade receivables, from an incurred loss method to a current expected credit loss method, otherwise known as “CECL.” The standard requires the measurement of expected credit losses to be based on relevant information, including historical experience, current conditions and a forecast that is supportable. The Company adopted the standard in the first quarter of 2020, with minimal impact to the Company’s financial results. As part of the adoption, the Company reviewed its’ portfolio of available-for-sale debt securities in an unrealized loss position, and assessed whether it intends to sell, or it is more likely than not that it will be required to sell before recovery of its’ amortized cost basis. The Company determined that is currently does not intend to sell these securities before recovery of their amortized cost basis. Additionally, the Company evaluated whether the decline in fair value has resulted from credit losses or other factors by considering the extent to which the fair value is less than amortized cost, any changes to the rating of the security by a rating agency, and adverse conditions specifically related to the security, among other factors. If this assessment indicates that a credit loss exists, the Company compares the present value of the cash flows expected to be collected against the amortized cost basis. A credit loss is recorded if the present value of the cash flows is less than the amortized cost basis, limited by the amount that the fair value is less than the amortized cost basis. Upon adoption, the Company did not record an allowance for credit losses on its available-for-sale debt securities. Additionally, the Company reviewed its open trade receivables arising from contractual coal sales. As part of its analysis, the Company performs periodic credit reviews of all active customers, reviews all trade receivables greater than 90 days past due, calculates historical loss rates and reviews current payment trends of all customers. Recent Accounting Guidance Issued Not Yet Effective In December 2019, the FASB issued ASU 2019-12, “Income Taxes (Topic 740) Simplifying the Accounting for Income Taxes.” ASU 2019-12 eliminates certain exceptions related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. The ASU is effective for public companies for fiscal years beginning after December 15, 2020, and interim periods therein with early adoption permitted. The Company is reviewing the provisions of the standard but does not expect a significant impact to the Company's financial statements. In March 2020, the FASB issued ASU 2020-04, "Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting." The amendments provide optional guidance for a limited time to ease the potential burden in accounting for reference rate reform. The new guidance provides optional expedients and exceptions for applying U.S. GAAP to contracts, hedging relationships and other transactions affected by reference rate reform if certain criteria are met. The amendments apply only to contracts and hedging relationships that reference LIBOR or another reference rate expected to be discontinued due to reference rate reform. These amendments are effective immediately and may be applied prospectively to contract modifications made and hedging relationships entered into or evaluated on or before December 31, 2022. We are currently evaluating our contracts and the optional expedients provided by the new standard.

Basis of Presentation (Policies)

6 Months Ended

Jun. 30, 2020

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States for interim financial reporting and U.S. Securities and Exchange Commission regulations. In the opinion of management, all adjustments, consisting of normal, recurring accruals considered necessary for a fair presentation, have been included. Results of operations for the three and six months ended June 30, 2020 are not necessarily indicative of results to be expected for the year ending December 31, 2020. These financial statements should be read in conjunction with the audited financial statements and related notes as of and for the year ended December 31, 2019 included in the Company’s Annual Report on Form 10-K filed with the U.S. Securities and Exchange Commission.

Effective May 15, 2020, Arch Coal, Inc. announced that its name changed to Arch Resources, Inc.

Recently Adopted Accounting Guidance

In June 2016, the FASB issued ASU 2016-13, “Financial Instruments-Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments,” and also issued subsequent amendments to the initial guidance under ASU 2018-19, ASU 2019-04 and ASU 2019-05. The standard modifies the measurement approach for credit losses on financial instruments, including trade receivables, from an incurred loss method to a current expected credit loss method, otherwise known as “CECL.” The standard requires the measurement of expected credit losses to be based on relevant information, including historical experience, current conditions and a forecast that is supportable. The Company adopted the standard in the first quarter of 2020, with minimal impact to the Company’s financial results.

As part of the adoption, the Company reviewed its’ portfolio of available-for-sale debt securities in an unrealized loss position, and assessed whether it intends to sell, or it is more likely than not that it will be required to sell before recovery of its’ amortized cost basis. The Company determined that is currently does not intend to sell these securities before recovery of their amortized cost basis. Additionally, the Company evaluated whether the decline in fair value has resulted from credit losses or other factors by considering the extent to which the fair value is less than amortized cost, any changes to the rating of the security by a rating agency, and adverse conditions specifically related to the security, among other factors. If this assessment indicates that a credit loss exists, the Company compares the present value of the cash flows expected to be collected against the amortized cost basis. A credit loss is recorded if the present value of the cash flows is less than the amortized cost basis, limited by the amount that the fair value is less than the amortized cost basis. Upon adoption, the Company did not record an allowance for credit losses on its available-for-sale debt securities.

Additionally, the Company reviewed its open trade receivables arising from contractual coal sales. As part of its analysis, the Company performs periodic credit reviews of all active customers, reviews all trade receivables greater than 90 days past due, calculates historical loss rates and reviews current payment trends of all customers.

Recent Accounting Guidance Issued Not Yet Effective

In December 2019, the FASB issued ASU 2019-12, “Income Taxes (Topic 740) Simplifying the Accounting for Income Taxes.” ASU 2019-12 eliminates certain exceptions related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. The ASU is effective for public companies for fiscal years beginning after December 15, 2020, and interim periods therein with early adoption permitted. The Company is reviewing the provisions of the standard but does not expect a significant impact to the Company's financial statements.

In March 2020, the FASB issued ASU 2020-04, "Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting." The amendments provide optional guidance for a limited time to ease the potential burden in accounting for reference rate reform. The new guidance provides optional expedients and exceptions for applying U.S. GAAP to contracts, hedging relationships and other transactions affected by reference rate reform if certain criteria are met. The amendments apply only to contracts and hedging relationships that reference LIBOR or another reference rate expected to be discontinued due to reference rate reform. These amendments are effective immediately and may be applied prospectively to contract modifications made and hedging relationships entered into or evaluated on or before December 31, 2022. We are currently evaluating our contracts and the optional expedients provided by the new standard.