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Summary of Significant Accounting Policies (Details) - USD ($) |  | 1 Months Ended | 2 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Jan. 29, 2021 | Dec. 31, 2019 | Aug. 31, 2020 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Nov. 06, 2020 | Feb. 15, 2017
Summary of Significant Accounting Policies Textuals |  |  |  |  |  |  |  |
Contribution amount to co-issuers |  |  | $ 100,000,000.0 |  |  |  |  |
Contribution to co-issuers, period with capital needs |  |  | 12 months |  |  |  |  |
Capitalized debt issuance costs related to Refinancing Transactions |  |  |  | $ 7,000,000.0 |  |  |  |
Gain on the settlement of claims |  |  |  |  |  | $ 12,800,000 |  |
Income tax provision |  |  |  | $ 8,000,000.0 | $ 46,000,000.0 | 18,400,000 |  |
Accounts receivable, payment term |  |  |  | 30 days |  |  |  |
Interest costs capitalized |  |  |  | $ 0 | 0 | 0 |  |
Royalty Expense |  |  |  | $ 214,700,000 | 388,600,000 | 474,300,000 |  |
Lease term |  |  |  | 10 years |  |  |  |
Minimum annual production of federal coal mining leases on original amount |  |  |  | 1.00% |  |  |  |
Monthly federal royalties payable from sale using surface mining methods |  |  |  | 12.50% |  |  |  |
Monthly federal royalties payable of production using underground mining methods |  |  |  | 8.00% |  |  |  |
Equity method investment |  |  |  | $ 0 | 0 | 0 |  |
Impairment of investment in equity security |  |  |  | 0 | 9,000,000.0 | 0 |  |
Restructuring charges for voluntary and involuntary workforce reductions |  |  |  | 37,900,000 | 24,300,000 | 1,200,000 |  |
Restructuring charges |  |  |  | 2,400,000 |  |  |  |
Asset impairment charges related to long-lived assets |  |  |  | 1,487,400,000 | 261,200,000 | 0 |  |
Foreign currency remeasurement gain (loss) |  |  |  | (4,000,000.0) | (2,700,000) | 1,400,000 |  |
Foreign currency translation adjustment |  |  |  | 6,100,000 | 200,000 | $ (5,900,000) |  |
Subsequent Event |  |  |  |  |  |  |  |
Summary of Significant Accounting Policies Textuals |  |  |  |  |  |  |  |
Payment for debt exchange | $ 9,400,000 |  |  |  |  |  |  |
Payment for debt exchange early tender premiums | 4,000,000.0 |  |  |  |  |  |  |
Debt exchange offer, required purchase amount (up to) | $ 22,500,000 |  |  |  |  |  |  |
Debt exchange offer, required purchase, percentage of accreted value | 80.00% |  |  |  |  |  |  |
Surety Bond |  |  |  |  |  |  |  |
Summary of Significant Accounting Policies Textuals |  |  |  |  |  |  |  |
Debt principal amount |  |  |  | $ 1,633,600,000 |  |  |  |
Pro Forma |  |  |  |  |  |  |  |
Summary of Significant Accounting Policies Textuals |  |  |  |  |  |  |  |
Income tax provision |  | $ 38,000,000 |  |  |  |  |  |
Surety Bond |  |  |  |  |  |  |  |
Summary of Significant Accounting Policies Textuals |  |  |  |  |  |  |  |
Transaction support agreements, additional collateral demands |  |  |  |  |  |  | $ 800,000,000 |
Transaction support agreements, percentage of Participating Sureties |  |  |  |  |  |  | 99.00% |
Transaction support agreements, additional collateral to be posted |  |  |  |  |  |  | $ 75,000,000.0 |
Debt instrument, transaction support agreements, fair value of second liens on mining equipment |  |  |  |  |  |  | 200,000,000.0 |
Transaction support agreements, additional collateral to be posted per year through 2024 |  |  |  |  |  |  | 25,000,000.0 |
Transaction support agreements, additional collateral term, free cash flow in any twelve-month period |  |  |  |  |  |  | 100,000,000.0 |
Transaction support agreements, additional collateral term, sale of assets benchmark (in excess of) |  |  |  |  |  |  | $ 10,000,000.0 |
Senior Notes | 6.000% Senior Secured Notes due March 2022 |  |  |  |  |  |  |  |
Summary of Significant Accounting Policies Textuals |  |  |  |  |  |  |  |
Stated interest rate |  |  |  | 6.00% |  |  |  |
Debt principal amount |  |  |  |  |  |  |  | $ 500,000,000.0
Long-term debt |  | $ 459,000,000.0 |  | $ 459,000,000.0 | $ 459,000,000.0 |  |  |
Senior Notes | 6.000% Senior Secured Notes due March 2022 | Subsequent Event |  |  |  |  |  |  |  |
Summary of Significant Accounting Policies Textuals |  |  |  |  |  |  |  |
Aggregate principal amount of debt exchanged | $ 398,700,000 |  |  |  |  |  |  |
Long-term debt | $ 60,300,000 |  |  |  |  |  |  |
Senior Notes | 10.00% Senior Secured Notes Due 2024 (New Co-Issuer Notes) | Subsequent Event |  |  |  |  |  |  |  |
Summary of Significant Accounting Policies Textuals |  |  |  |  |  |  |  |
Stated interest rate | 10.00% |  |  |  |  |  |  |
Debt principal amount | $ 193,900,000 |  |  |  |  |  |  |
Senior Notes | 8.500% Senior Secured Notes due 2024 (New Peabody Notes) | Subsequent Event |  |  |  |  |  |  |  |
Summary of Significant Accounting Policies Textuals |  |  |  |  |  |  |  |
Stated interest rate | 8.50% |  |  |  |  |  |  |
Debt principal amount | $ 195,100,000 |  |  |  |  |  |  |
Senior Notes | New Co-Issuer Term Loans | Subsequent Event |  |  |  |  |  |  |  |
Summary of Significant Accounting Policies Textuals |  |  |  |  |  |  |  |
Stated interest rate | 10.00% |  |  |  |  |  |  |
Debt amount incurred | $ 206,000,000.0 |  |  |  |  |  |  |
Line of Credit | Revolving Credit Facility | Subsequent Event |  |  |  |  |  |  |  |
Summary of Significant Accounting Policies Textuals |  |  |  |  |  |  |  |
Repayments of lines of credit | 10,000,000.0 |  |  |  |  |  |  |
Line of Credit | Letter of Credit | Subsequent Event |  |  |  |  |  |  |  |
Summary of Significant Accounting Policies Textuals |  |  |  |  |  |  |  |
Debt amount incurred | $ 324,000,000.0 |  |  |  |  |  |  |
Revolving credit facility, fee on unused borrowings | 6.00% |  |  |  |  |  |  |
Commitment fee percentage | 0.50% |  |  |  |  |  |  |
Debt covenant, aggregate liquidity at the end of each quarter | $ 125,000,000.0 |  |  |  |  |  |  |
Middlemount |  |  |  |  |  |  |  |
Summary of Significant Accounting Policies Textuals |  |  |  |  |  |  |  |
Ownership percentage of equity method investment |  |  |  | 50.00% |  |  |  |
Minimum | Machinery and equipment |  |  |  |  |  |  |  |
Summary of Significant Accounting Policies Textuals |  |  |  |  |  |  |  |
Useful life |  |  |  | 1 year |  |  |  |
Maximum | Buildings and improvements |  |  |  |  |  |  |  |
Summary of Significant Accounting Policies Textuals |  |  |  |  |  |  |  |
Useful life |  |  |  | 32 years |  |  |  |
Maximum | Machinery and equipment |  |  |  |  |  |  |  |
Summary of Significant Accounting Policies Textuals |  |  |  |  |  |  |  |
Useful life |  |  |  | 15 years |  |  |  |

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