Warrior Met Coal (HCC) 10-K 24 Feb 21 2020 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Feb. 22, 2021	Jun. 30, 2020
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-38061
Entity Registrant Name	Warrior Met Coal, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	81-0706839
Entity Address, Address Line One	16243 Highway 216
Entity Address, City or Town	Brookwood
Entity Address, State or Province	AL
Entity Address, Postal Zip Code	35444
City Area Code	205
Local Phone Number	554-6150
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
ICFR Auditor Attestation Flag	true
Entity Public Float			$ 787.7
Entity Common Stock, Shares Outstanding (in shares)		51,342,601
Documents Incorporated by Reference	Portions of the registrant’s definitive proxy statement for its 2020 Annual Meeting of Stockholders, which will be filed with the Securities and Exchange Commission within 120 days of December 31, 2020, are incorporated by reference into Part III of this report for the year ended December 31, 2020.
Entity Central Index key	0001691303
Document Fiscal Year Focus	2020
Amendment Flag	false
Document Fiscal Period Focus	FY
Common Stock, par value $0.01 per share
Document Information [Line Items]
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	HCC
Security Exchange Name	NYSE
Rights to Purchase Series A Junior Participating Preferred Stock, par value $0.01 per share
Document Information [Line Items]
Title of 12(b) Security	Rights to Purchase Series A Junior Participating Preferred Stock, par value $0.01 per share
Security Exchange Name	NYSE
No Trading Symbol Flag	true

BALANCE SHEETS

BALANCE SHEETS - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 211,916,000	$ 193,383,000
Short-term investments	8,504,000	14,675,000
Trade accounts receivable	83,298,000	99,471,000
Other receivables	5,142,000	1,847,000
Income tax receivable	0	12,925,000
Inventories, net	118,713,000	97,901,000
Prepaid expenses and other	39,910,000	23,844,000
Total current assets	467,483,000	444,046,000
Mineral interests, net	100,855,000	110,130,000
Property, plant and equipment, net	637,108,000	606,200,000
Non-current income tax receivable	0	11,349,000
Deferred income taxes	174,372,000	154,297,000
Other long-term assets	14,118,000	18,242,000
Total assets	1,393,936,000	1,344,264,000
Current liabilities:
Accounts payable	59,110,000	46,436,000
Accrued expenses	86,108,000	65,755,000
Asset retirement obligations	4,354,000	2,623,000
Short-term financing lease obligations	14,385,000	10,146,000
Other current liabilities	6,361,000	3,992,000
Total current liabilities	170,318,000	128,952,000
Long-term debt	379,908,000	339,189,000
Asset retirement obligations	57,553,000	53,583,000
Black lung obligations	34,567,000	30,233,000
Financing lease obligations	24,091,000	25,528,000
Other long-term liabilities	2,258,000	1,197,000
Total liabilities	668,695,000	578,682,000
Stockholders’ Equity:
Common stock, $0.01 par value per share (Authorized -140,000,000 shares, 53,408,040 issued and 51,186,199 outstanding as of December 31, 2020 and 53,293,449 issued and 51,071,608 outstanding as of December 31, 2019)	534,000	533,000
Preferred stock, $0.01 par value per share (10,000,000 shares authorized, no shares issued and outstanding)	0	0
Treasury stock, at cost (2,221,841 shares as of December 31, 2020 and December 31, 2019)	(50,576,000)	(50,576,000)
Additional paid in capital	249,746,000	243,932,000
Retained earnings	525,537,000	571,693,000
Total stockholders’ equity	725,241,000	765,582,000
Total liabilities and stockholders’ equity	$ 1,393,936,000	$ 1,344,264,000

BALANCE SHEETS (Parenthetical)

BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Common stock par value (in dollars per share)	$ 0.01	$ 0.01
Common stock shares authorized (in shares)	140,000,000	140,000,000
Common stock shares issued (in shares)	53,408,040	53,293,449
Common stock shares outstanding (in shares)	51,186,199	51,071,608
Preferred stock par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock shares authorized (in shares)	10,000,000	10,000,000
Preferred stock shares issued (in shares)	0	0
Preferred stock shares outstanding (in shares)	0	0
Treasury stock (in shares)	2,221,841	2,221,841

STATEMENTS OF OPERATIONS

STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues:
Total revenues	$ 782,738	$ 1,268,309	$ 1,378,007
Costs and expenses:
Cost of sales (exclusive of items shown separately below)	625,170	720,745	716,645
Cost of other revenues (exclusive of items shown separately below)	33,736	29,828	10,172
Depreciation and depletion	118,092	97,330	97,209
Selling, general and administrative	32,879	37,014	36,626
Transaction and other costs	0	0	9,068
Total costs and expenses	809,877	884,917	869,720
Operating (loss) income	(27,139)	383,392	508,287
Interest expense, net	(32,310)	(29,335)	(37,314)
Loss on early extinguishment of debt	0	(9,756)	0
Other income	3,544	22,815	0
(Loss) income before income taxes	(55,905)	367,116	470,973
Income tax (benefit) expense	(20,144)	65,417	(225,814)
Net (loss) income	$ (35,761)	$ 301,699	$ 696,787
Basic and diluted net (loss) income per share:
Net (loss) income per share—basic (in dollars per share)	$ (0.70)	$ 5.87	$ 13.19
Net (loss) income per share—diluted (in dollars per share)	$ (0.70)	$ 5.86	$ 13.17
Weighted average number of shares outstanding—basic (in shares)	51,168	51,363	52,812
Weighted average number of shares outstanding— diluted (in shares)	51,168	51,493	52,918
Dividends per share (in dollars per share)	$ 0.20	$ 4.61	$ 6.73
Sales
Revenues:
Total revenues	$ 761,871	$ 1,235,998	$ 1,342,683
Other revenues
Revenues:
Total revenues	$ 20,867	$ 32,311	$ 35,324

STATEMENTS OF CHANGES IN EQUITY

STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Common Stock	Preferred Stock	Treasury Stock	Additional Paid in Capital	Retained Earnings
Balance at beginning of period at Dec. 31, 2017	$ 413,023	$ 534	$ 0	$ 0	$ 329,993	$ 82,496
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	696,787					696,787
Dividends paid	(360,635)				(91,122)	(269,513)
Stock compensation	6,405				6,405
Treasury stock purchase	(38,030)			(38,030)
Other	(4,938)	(1)			(5,449)	512
Balance at end of period at Dec. 31, 2018	712,612	533	0	(38,030)	239,827	510,282
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	301,699					301,699
Dividends paid	(240,394)					(240,394)
Stock compensation	5,349				5,349
Treasury stock purchase	(12,546)			(12,546)
Other	(1,138)				(1,244)	106
Balance at end of period at Dec. 31, 2019	765,582	533	0	(50,576)	243,932	571,693
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(35,761)					(35,761)
Dividends paid	(10,395)					(10,395)
Stock compensation	7,087				7,087
Other	(1,272)	1			(1,273)
Balance at end of period at Dec. 31, 2020	$ 725,241	$ 534	$ 0	$ (50,576)	$ 249,746	$ 525,537

STATEMENTS OF CHANGES IN EQUI_2

STATEMENTS OF CHANGES IN EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Stockholders' Equity [Abstract]
Dividends per share (in dollars per share)	$ 0.20	$ 4.61	$ 6.73

STATEMENTS OF CASH FLOWS

STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended				12 Months Ended			43 Months Ended
	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020
OPERATING ACTIVITIES
Net (loss) income	$ (33,711)	$ 21,545	$ 20,751	$ 110,447	$ (35,761)	$ 301,699	$ 696,787
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Depreciation and depletion					118,092	97,330	97,209
Deferred income tax (benefit) expense					(20,075)	68,483	(223,038)
Stock-based compensation expense					7,602	5,820	6,405
Amortization of debt issuance costs and debt discount, net					1,546	1,361	2,486
Accretion and valuation adjustment of ARO					2,631	(7,891)	(19,942)
Loss on early extinguishment of debt				9,800	0	9,756	0
Changes in operating assets and liabilities:
Trade accounts receivable					16,173	38,928	(20,653)
Other receivables					(3,308)	(224)	3,872
Income tax receivable	(6,600)				24,274	21,795	(12,431)
Inventories					(13,465)	(30,491)	(1,812)
Prepaid expenses and other current assets					(16,066)	4,088	1,444
Accounts payable					15,361	13,409	5,060
Accrued expenses and other current liabilities					(3,936)	(17,317)	13,835
Non-current income tax receivable					0	0	17,945
Other					19,558	26,068	(7,771)
Net cash provided by operating activities					112,626	532,814	559,396
INVESTING ACTIVITIES
Purchase of property, plant and equipment					(87,488)	(107,278)	(101,620)
Deferred mine development costs					(27,093)	(23,392)	(8,937)
Proceeds from sale of property, plant and equipment					159	3,127	2,928
Sale of short-term investments					14,733	17,501	0
Purchases of short-term investments					(8,500)	(24,171)	0
Net cash used in investing activities					(108,189)	(134,213)	(107,629)
FINANCING ACTIVITIES
Dividends paid					(10,395)	(240,394)	(360,635)	$ (39,500)
Proceeds from issuance of debt					0	0	128,750
Borrowings under ABL Facility					70,000	0	0
Repayments under ABL Facility					(30,000)	0	0
Retirements of debt					0	(140,272)	(3,060)
Principal repayments of financing lease obligations					(14,237)	(17,273)
Debt issuance costs paid					0	0	(3,713)
Common shares repurchased					0	(12,546)	(38,030)
Other					(1,272)	(1,138)	(4,938)
Net cash provided by (used in) financing activities					14,096	(411,623)	(281,626)
Net increase (decrease) in cash and cash equivalents and restricted cash					18,533	(13,022)	170,141
Cash and cash equivalents and restricted cash at beginning of period		$ 193,383		$ 206,405	193,383	206,405	36,264
Cash and cash equivalents and restricted cash at end of period	$ 211,916		$ 193,383		211,916	193,383	206,405	$ 211,916
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Interest paid, net of capitalized interest					30,523	33,544	30,237
Cash paid for income taxes					69	85	3
SUPPLEMENTAL DISCLOSURE OF NON-CASH INVESTING AND FINANCING ACTIVITIES:
Financing leases - equipment					$ 18,967	$ 45,523	$ 6,822

Business and Basis of Presentat

Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business and Basis of Presentation	Business and Basis of Presentation Description of the Business Warrior Met Coal, Inc. (the "Company") is a U.S.-based, environmentally and socially minded supplier to the global steel industry. The Company is dedicated entirely to mining non-thermal metallurgical (met) coal used as a critical component of steel production by metal manufacturers in Europe, South America and Asia. The Company is a large-scale, low-cost producer and exporter of premium met coal, also known as hard-coking coal ("HCC"), operating highly efficient longwall operations in its underground mines based in Alabama. The HCC that the Company produces from the Blue Creek coal seam contains very low sulfur, has strong coking properties and is of a similar quality to coal referred to as the premium HCC produced in Australia. The Company also generates ancillary revenues from the sale of natural gas extracted as a byproduct from the underground coal mines and royalty revenues from leased properties. Basis of Presentation The accompanying consolidated financial statements include the accounts of Warrior Met Coal, Inc and its subsidiaries (the "Company"). All significant intercompany transactions and balances have been eliminated in consolidation. Impact of the COVID-19 Pandemic Upon our Financial Condition and Results of Operations The global steelmaking industry's demand for met coal is affected by pandemics, epidemics or other public health emergencies, such as the recent outbreak of the novel coronavirus ("COVID-19"), which has spread from China to many other countries including the United States. In March 2020, the World Health Organization ("WHO") declared COVID-19 a pandemic, and the President of the United States declared the COVID-19 outbreak a national emergency. The outbreak has resulted in governments around the world implementing stringent measures to help control the spread of the virus, including quarantines, "shelter in place" and "stay at home" orders, travel restrictions, business curtailments, school closures, and other measures. In addition, governments and central banks in several parts of the world have enacted fiscal and monetary stimulus measures to counteract the impacts of COVID-19. The Company operates in a critical infrastructure industry, as defined by the U.S. Department of Homeland Security. As such, the Company continues to operate its mines in a safe manner under the guidelines issued by the Centers for Disease Control and Prevention and the Alabama State Health Department. In response to these measures and for the protection of employees, the Company has taken steps to ensure our employees remain safe. As of the filing of this Form 10-K, the Company has not had to idle or temporarily idle its mines. Notwithstanding our continued operations, COVID-19 has had and may continue to have further negative impacts on our two operating mines, supply chain, transportation networks and customers, which may continue to compress our margins, and reduce demand for the met coal that we produce. The COVID-19 outbreak is a widespread public health crisis that is adversely affecting the economies and financial markets of many countries, including those of our customers, which are primarily located in Europe, South America and Asia. A prolonged economic downturn could adversely affect demand for our met coal and contribute to volatile supply and demand conditions affecting prices and volumes. The progression of COVID-19 could also negatively impact our business or results of operations through the temporary closure of one of our mines, customers or critical suppliers, or the McDuffie Coal Terminal at the Port of Mobile in Alabama, or a disruption to our rail and barge carriers, which would delay or prevent deliveries to our customers, among others. In addition, the ability of our employees and our suppliers' and customers' employees to work may be significantly impacted by individuals contracting or being exposed to COVID-19, or as a result of the control measures noted above, which may significantly affect the demand for met coal. Our customers may be directly impacted by business curtailments or weak market conditions and may not be willing or able to fulfill their contractual obligations or open letters of credit. We may also experience delays in obtaining letters of credit or processing letter of credit payments due to the impacts of COVID-19 on foreign issuing and U.S. intermediary banks. Furthermore, the progression of, and global response to, the COVID-19 outbreak has begun to cause, and increases the risk of, further delays in construction activities and equipment deliveries related to our capital projects, including potential delays in obtaining permits from government agencies. The extent of such delays and other

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Use of Estimates The Company prepares its financial statements in conformity with GAAP, which requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the periods presented. Due to the inherent uncertainty involved in making estimates, actual results could differ from those estimates. Concentrations of Credit Risk and Major Customers The Company’s principal line of business is mining and marketing met coal to foreign steel producers. For the year ended December 31, 2020, approximately 97.3% of sales were derived from coal shipments to customers, located primarily in Europe, South America and Asia. At December 31, 2020 approximately 96.8% of trade receivables were related to these customers. For the year ended December 31, 2020, our geographic customer mix was 56% in Europe, 25% in South America and 19% in Asia. During the year ended December 31, 2020, Xcoal Energy & Resources, Exiros BV Sucursal Uruguay, and Iskenderun Demir Ve Celik A.S. accounted for $146.5 million, or 18.7%, $117.7 million, or 15.0%, and $89.1 million, or 11.4% of total revenues, respectively. During the year ended December 31, 2019, Xcoal Energy & Resources, Exiros BV Sucursal Uruguay, ArcelorMittal, and Thyssenkrupp Steel Europe AG accounted for $276.2 million, or 22.3%, $159.6 million, or 12.9%, $128.2 million, or 10.4% and $125.5 million, or 10.1% of total revenues, respectively. During the year ended December 31, 2018, Xcoal Energy & Resources, Exiros BV Sucursal Uruguay and Huettenwerke Krupp Mannesmann GmbH accounted for $203.6 million, or 15.1%, $148.5 million, or 11.0%, and $141.3 million, or 10.5% of total revenues, respectively. Revenue Recognition Revenue is recognized when performance obligations under the terms of a contract with our customers are satisfied; for all contracts this occurs when control of the promised goods have been transferred to our customers. For coal shipments to domestic customers via rail, control is transferred when the railcar is loaded. For coal shipments to international customers via ocean vessel, control is transferred when the vessel is loaded at the Port of Mobile in Alabama. For natural gas sales, control is transferred when the gas has been transferred to the pipeline. Revenue is disaggregated between coal sales within the Company's mining segment and natural gas sales included in all other revenues, as disclosed in Note 20. Our coal and gas sales generally include up to 45-day payment terms following the transfer of control of the goods to the customer. We typically do not include extended payment terms in our contracts with customers. Trade Accounts Receivable and Allowance for Credit Losses Trade accounts receivable represent customer obligations that are derived from revenue recognized from contracts with customers. Credit is extended based on an evaluation of the individual customer's financial condition. The Company maintains trade credit insurance on the majority of its customers and the geographic regions of coal shipments to these customers. In some instances, the Company requires letters of credit, cash collateral or prepayments from its customers on or before shipment to mitigate the risk of loss. These efforts have consistently resulted in the Company recognizing no historical credit losses. The Company also has never had to have a claim against its trade credit insurance policy. In order to estimate the allowance for credit losses on trade accounts receivable, the Company utilizes an aging approach in which potential impairment is calculated based on how long a receivable has been outstanding (e.g., current, 1-31, 31-60, etc.). The Company calculates an expected credit loss rate based on the Company’s historical credit loss rate, the risk characteristics of our customers, and the current metallurgical coal and steel market environments. As of December 31, 2020, the estimated allowance for credit losses was immaterial and did not have a material impact on the Company's financial statements. Shipping and Handling Costs incurred to transport coal to the point of sale at the Port of Mobile, Alabama, are included in cost of sales and the gross amounts billed to customers, if any, to cover shipping and handling to the ultimate/final destination are included in sales. Cash and Cash Equivalents Cash and cash equivalents include short-term deposits and highly liquid investments that have original maturities of three months or less when purchased and are stated at cost, which approximates fair value. Short-Term Investments Instruments with maturities greater than three months, but less than twelve months, are included in short-term investments. The Company purchases United States Treasury bills with maturities ranging from six to twelve months which are classified as held to maturity and are carried at amortized cost, which approximates fair value. The Company also purchases fixed income securities and certificates of deposits with varying maturities that are classified as available for sale and are carried at fair value. Securities classified as held to maturity securities are those securities that management has the intent and ability to hold to maturity. As of December 31, 2020 and 2019, the Company’s short-term investments of $8.5 million and $14.7 million, respectively, consisted of cash and fixed income securities. The short-term investments are posted as collateral for the self-insured black lung related claims asserted by or on behalf of former employees of Walter Energy, Inc. ("Walter Energy") and its subsidiaries, which were assumed by the Company and relate to periods prior to March 31, 2016. Inventories Inventories are valued at the lower of cost or net realizable value. Coal inventory costs include labor, supplies, equipment costs, operating overhead, freight, royalties, depreciation and depletion and other related costs. Coal inventories are valued using the first-in, first-out (“FIFO”) inventory valuation method. The valuation of coal inventories is subject to estimates due to possible gains and losses resulting from inventory movements from the mine site to storage facilities, inherent inaccuracies in belt scales and aerial surveys used to measure quantities and fluctuations in moisture content. Periodic adjustments to coal tonnages on hand are made for an estimate of coal shortages and overages due to these inherent gains and losses, primarily based on historical results from aerial surveys and periodic coal pile clean-ups. Supplies inventories are valued using the average cost method of accounting. Management evaluates its supplies inventory in terms of excess and obsolete exposures which includes such factors as anticipated usage, inventory turnover, inventory levels and ultimate market value. A reserve for excess and obsolete supplies inventory is established and charged to cost of sales in the Statements of Operations. Deferred Longwall Move Expenses Direct costs, including labor and supplies, associated with moving longwall equipment and the related equipment refurbishment costs are deferred and included in prepaid expenses. These deferred costs are amortized on a units-of-production basis into cost of sales over the life of the subsequent panel of coal mined by the longwall equipment. See Note 4 for further disclosures related to deferred longwall move expenses. Advanced Mining Royalties Lease rights to coal reserves are often acquired in exchange for royalty payments. Advance mining royalties are advance payments made to lessors under terms of mineral lease agreements that are recoupable against future production royalties. These advance payments are deferred and charged to operations as the coal reserves are mined. Advance mining royalties are included in other long-term assets. Property, Plant and Equipment Property, Plant and Equipment Property, plant and equipment are recorded at cost. Depreciation is recorded principally on the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized on the straight-line method over the lesser of the useful life of the improvement or the remaining lease term. Estimated useful lives used in computing depreciation expense range from three fifteen Deferred Mine Development Costs of developing new underground mines and certain underground expansion projects are capitalized. Underground development costs, which are costs incurred to make the coal physically accessible, may include construction permits and licenses, mine design, construction of access roads, main entries, airshafts, roof protection and other facilities. Mine development costs are amortized primarily on a units-of-production basis over the estimated reserve tons directly benefiting from the capital expenditures. Costs amortized during the production phase of a mine are capitalized into inventory and expensed to cost of sales as the coal is sold. Coal sales revenue related to incidental production during the development phase are recorded as sales with an offset to cost of sales based on the estimated cost per ton sold for the mine when the asset is in place for its intended use. Owned and Leased Mineral Interests Costs to obtain coal reserves and lease mineral rights are capitalized based on cost or the fair value at acquisition and depleted using the units-of-production method over the life of proven and probable reserves. Lease agreements are generally long-term in nature (original terms range from 10 to 50 years) and substantially all of the leases contain provisions that allow for automatic extension of the lease term provided certain requirements are met. Depletion expense was $9.3 million, $9.9 million, and $9.6 million for the years ended December 31, 2020, December 31, 2019, and December 31, 2018, respectively, and is included in depreciation and depletion in the accompanying Statements of Operations. Asset Retirement Obligations The Company has certain asset retirement obligations primarily related to mine closing reclamation costs, perpetual water care costs and other costs associated with dismantling and removing facilities. Asset retirement obligations are determined for each mine using various estimates and assumptions, including estimates of disturbed acreage as determined from engineering data, estimates of future costs to reclaim the disturbed acreage and the timing of related cash flows, discounted using a credit-adjusted, risk-free rate. The Company's asset retirement obligations also include estimates to reclaim gas wells in accordance with the Oil and Gas Board of Alabama. On at least an annual basis, the Company reviews the entire asset retirement obligation liability and makes necessary adjustments for permit changes, the anticipated timing of mine closures, and revisions to cost estimates and productivity assumptions to reflect current experience. As changes in estimates occur, the carrying amount of the obligation and asset are revised to reflect the new estimate after applying the appropriate credit-adjusted, risk-free discount rate. The future costs of these obligations are accrued at the estimated fair value in the period in which they are incurred if a reasonable estimate of fair value can be made. The present value of the estimated asset retirement cost is capitalized as part of the carrying amount of the long-lived asset. For sites where there is no asset, expense or income is recognized for changes in estimates. Capitalized asset retirement costs are amortized on a units-of-production basis over the estimated reserves. Accretion of the asset retirement obligation is recognized over time and generally will escalate over the life of the producing asset, typically as production declines. Accretion is included in cost of sales on the Statements of Operations. Accrued mine closing costs, perpetual care costs and reclamation costs and other costs of dismantling and removing facilities are regularly reviewed by management and revised for changes in future estimated costs and regulatory requirements, as necessary. For ongoing operations, adjustments to the liability result in an adjustment to the corresponding asset. For some operations, adjustments to the liability are recognized as income or expense in the period the adjustment is recorded as no asset was recorded to offset the liability established during acquisition accounting related to the acquisition of certain assets of Walter Energy as the operations were idle at that time. Any difference between the recorded obligation and the actual cost of reclamation is recorded in profit or loss in the period the obligation is settled. See Note 8 for further disclosures related to asset retirement obligations. Impairment of Long-Lived Assets Property, plant and equipment and other long-lived assets are reviewed for impairment at least annually or whenever events or changes in circumstances indicate that the book value of the asset may not be recoverable. The Company periodically evaluates whether events and circumstances have occurred that would indicate possible impairment. When impairment indicators exist, the Company uses an estimate of the future undiscounted cash flows of the related asset or asset group over the remaining life in measuring whether or not the asset values are recoverable. If the carrying amount of an asset or asset group exceeds its estimated future cash flows, impairment is recognized equal to the amount by which the carrying amount of the asset exceeds the fair value of the asset or asset group. Fair value is generally determined using market quotes, if available, or a discounted cash flow approach. The Company’s estimate of future undiscounted cash flows is based on assumptions including long-term met coal pricing forecasts, anticipated production volumes and mine operating costs for the life of the mine or estimated useful life of the asset. Equity Award Compensation The Company accounts for equity award-based compensation to employees and non-employee/directors in accordance with ASC 718 requiring employee equity awards to be accounted for under the fair value method. The Company recognizes forfeitures as they occur. The Company recognizes compensation expense associated with equity awards for all awards made to employees as the requisite service, performance and market vesting conditions are met. For units granted containing only service and performance conditions, the fair value of the award is equal to the market price of the Company's common stock at the date of grant. For units granted containing only a market condition, the fair value of the award is determined utilizing a Monte Carlo simulation model which incorporates the total stockholder return hurdles set for each grant. Compensation expense for equity awards with a service-only condition is recognized over the employee’s requisite service period using a graded vesting method. For awards with a performance condition that affects vesting, the performance condition is not considered in determining the award’s grant-date fair value; however, the performance conditions are considered when estimating the quantity of awards that are expected to vest. No compensation expense is recorded for awards with performance conditions until the performance condition is determined to be probable of achievement. For awards with a market condition that affects vesting, the market condition is considered in determining the award’s grant-date fair value. Compensation expense for awards with a market condition is recognized straight-line over the derived or implied service period. Compensation expense for equity awards is included in cost of sales (exclusive of items shown separately below) and selling, general and administrative in the accompanying Statements of Operations. Deferred Financing Costs The costs to obtain new debt financing or amend existing financing agreements are deferred and amortized to interest expense over the life of the related indebtedness or credit facility using the straight-line method. As of December 31, 2020 and December 31, 2019, there were $2.7 million of unamortized origination fees related to the ABL Facility (as defined in Note 13) in other long-term assets on the accompanying Balance Sheet. As of December 31, 2020 and December 31, 2019 there were $3.5 million and $4.2 million, respectively, of unamortized deferred financing costs and debt discount, net, related to the Notes (as defined in Note 13), which is presented as a net deduction from the carrying amount of the debt recognized in the accompanying Balance Sheet. Income Taxes The Company records a tax provision for the expected tax effects of the reported results of operations. The provision for income taxes is determined using the asset and liability method, under which deferred tax assets and liabilities are recognized for the expected future tax impact of temporary differences between the financial reporting and tax bases of assets and liabilities, and for operating losses and tax credit carryforwards. Deferred income tax assets and liabilities are measured using the currently enacted tax rates that apply to taxable income in effect for the years in which those tax assets and liabilities are expected to be realized or settled. The Company records a valuation allowance to reduce deferred income tax assets to the amount that is believed more likely than not to be realized. When the Company concludes that all or part of the net deferred income tax assets are not realizable in the future, the Company makes an adjustment to the valuation allowance that is charged to earnings in the period that such determination was made. The Company recognizes tax benefits from uncertain tax positions only if it is more likely than not that the tax position will be sustained on examination by the taxing authorities, based on the technical merits of the position. The tax benefits recognized in the financial statements from such positions are then measured based on the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement. Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. A three level hierarchy has been established for valuing assets and liabilities based on how transparent (observable) the inputs are that are used to determine fair value, with the inputs considered most observable categorized as Level 1 and those that are the least observable categorized as Level 3. Hierarchy levels are defined as follows: Level 1: Quoted prices in active markets for identical assets and liabilities. Level 2: Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. Level 3: Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. Leases The Company determines if an arrangement is a lease at inception. The Company has an accounting policy election that leases with an initial term of 12 months or less remain off its balance sheet and lease payments are recognized in the Statements of Operations on a straight-line basis over the lease term. A right-of-use asset represents the Company's right to use an underlying asset for the lease term and lease liabilities represent its obligation to make lease payments arising from the lease. Operating lease right-of-use assets and liabilities are recognized at the lease commencement date based on the present value of the lease payments over the lease term. For purpose of calculating such present values, lease payments include components that vary based on an index or rate, using the prevailing index or rate at the commencement date and exclude components that vary based upon other factors. For those leases that do not contain a readily determinable implicit rate, the Company uses its incremental borrowing rate at commencement to determine the present value of lease payments. Variable lease payments not included within lease contracts are expensed as incurred. The Company's leases may include options to extend or terminate the lease, and such options are reflected in the term when their exercise is reasonably certain. Lease expense is recognized on a straight-line basis over the lease term. New Accounting Pronouncements The Company adopted Accounting Standards Update ("ASU") 2016-13, "Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments" as of January 1, 2020 using the modified retrospective approach. The ASU requires the use of an “expected loss” model for instruments measured at amortized cost, in which companies will be required to estimate the lifetime expected credit loss and record an allowance to offset the amortized cost basis, resulting in a net presentation of the amount expected to be collected on the financial asset. The adoption of the new standard did not have a material impact on the Company's financial statements, including accounting policies, processes and systems. In December 2019, the Financial Accounting Standards Board ("FASB") issued ASU 2019-12, “Income Taxes (Topic 740) - Simplifying the Accounting for Income Taxes,” which is intended to simplify various aspects related to accounting for income taxes. This ASU removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The ASU is effective for fiscal years beginning after December 15, 2020. The Company expects to adopt the standard as of January 1, 2021 with no material impact to the Company's results of operations, financial condition, cash flows or financial statement presentation.

Inventories, net

Inventories, net	12 Months Ended
	Dec. 31, 2020
Inventory Disclosure [Abstract]
Inventories, net	Inventories, net Inventories, net are summarized as follows (in thousands): December 31, 2020 December 31, 2019 Coal $ 86,272 $ 69,064 Raw materials, parts, supplies and other, net 32,441 28,837 Total inventories, net $ 118,713 $ 97,901

Prepaid Expenses and Other

Prepaid Expenses and Other	12 Months Ended
	Dec. 31, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid Expenses and Other	Prepaid Expenses and Other Prepaid expenses and other consisted of the following (in thousands): December 31, 2020 December 31, 2019 Deferred longwall move expenses $ 22,972 $ 15,621 Prepaid insurance 3,832 3,631 Prepaid deposits 6,937 345 Other 6,169 4,247 Total prepaid expenses and other $ 39,910 $ 23,844

Mineral Interests and Property,

Mineral Interests and Property, Plant and Equipment, Net	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Mineral Interests and Property, Plant and Equipment, net	Mineral Interests and Property, Plant and Equipment, net Mineral interests totaled $144.2 million and $144.2 million and the related accumulated depletion totaled $43.4 million and $34.1 million as of December 31, 2020 and December 31, 2019, respectively. Property, plant and equipment are summarized as follows (in thousands): December 31, 2020 December 31, 2019 Land $ 71,886 $ 72,267 Land improvements 18,024 18,026 Building and leasehold improvements 77,556 74,342 Mine development and infrastructure costs 29,893 13,315 Machinery and equipment 679,393 614,687 Financing lease right of use asset 56,528 44,996 Construction in progress 82,367 42,106 Total 1,015,647 879,739 Less: Accumulated depreciation (378,539) (273,539) Property, plant and equipment, net $ 637,108 $ 606,200 Depreciation and depletion expense was $118.1 million, $97.3 million, and $97.2 million, for the years ended December 31, 2020 and December 31, 2019, and December 31, 2018, respectively.

Other Long-Term Assets

Other Long-Term Assets	12 Months Ended
	Dec. 31, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Other Long-Term Assets	Other Long-Term AssetsOther long-term assets consisted of the following (in thousands): December 31, 2020 December 31, 2019 Advance mining royalties $ 7,305 $ 8,976 ABL Facility origination fees 2,667 2,723 Other 4,146 6,543 Total other long-term assets $ 14,118 $ 18,242

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes On March 27, 2020, former President Trump signed and enacted into law the Coronavirus Aid, Relief and Economic Security Act (the "CARES Act"). The CARES Act, among other things, provides temporary relief from certain aspects of the Tax Cuts and Jobs Act of 2017 that had imposed limitations on the utilization of certain losses, interest expense deductions and alternative minimum tax ("AMT") credits. The CARES Act also provides opportunities for businesses to improve their cash flows by obtaining refunds for prior taxable years and reducing their income and deferring payroll tax liabilities for the current taxable year. Specifically, Section 2305 of the CARES Act accelerates the ability to receive refunds of remaining AMT credits for tax years 2019, 2020 and 2021. During the third quarter of 2020, the Company received approximately $24.3 million for refunds of AMT credits. As of December 31, 2020, the Company had no current income tax receivable and no non-current income tax receivable for AMT credits. Income Tax (Benefit) Expense Income tax (benefit) expense consisted of the following (in thousands): For the years ended December 31, 2020 2019 2018 Current Federal $ (74) $ (3,151) $ (2,776) State 5 85 — (69) (3,066) (2,776) Deferred Federal (16,731) 53,677 (176,141) State (3,344) 14,806 (46,897) (20,075) 68,483 (223,038) Total $ (20,144) $ 65,417 $ (225,814) For the year ended December 31, 2020, we recognized an income tax benefit of $20.1 million or an effective tax rate of 36.0%. Total income tax (benefit) expense differs from the expected tax (benefit) expense (computed by multiplying the U.S. federal statutory rate of 21% by (loss) income before income taxes) as a result of the following (in thousands): For the years ended December 31, 2020 2019 2018 (Loss) income before income tax (benefit) expense $ (55,905) $ 367,116 $ 470,973 Tax (benefit) expense at statutory tax rate (11,740) 77,094 98,904 Effect of: Depletion (1,504) (16,198) (18,227) Tax Cuts and Jobs Act impact — — (2,775) State and local income tax, net of federal effect (2,637) 11,747 14,897 Valuation allowance on deferred tax assets — — (312,493) Non-deductible transaction costs — — 566 Impact of Walter Energy IRS Settlement (1) — (6,615) — IRC Section 451 marginal well credit (3,977) — (4,964) Other (286) (611) (1,722) Tax (benefit) expense recognized $ (20,144) $ 65,417 $ (225,814) (1) In the fourth quarter of 2019, an adjustment of $6.6 million was recorded to recognize additional alternative minimum tax credits, general business credits and NOLs available to the Company in connection with a settlement agreement between Walter Energy and the Internal Revenue Service. Deferred Taxes Deferred income tax assets and liabilities reflect the effects of tax losses, credits, and the future income tax effects of temporary differences between the financial statement carrying amounts of assets and liabilities and their respective tax bases. Deferred income tax assets and liabilities are measured using enacted tax rates that apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. Significant components of the Company's deferred income tax assets and liabilities were (in thousands): December 31, 2020 December 31, 2019 Deferred income tax assets: Net operating loss and credit carryforwards $ 253,756 $ 215,805 Inventory — 457 Asset retirement obligations 15,547 14,115 Black lung obligations 9,275 8,168 Accrued expenses 4,303 5,597 Other 3,614 3,649 Total deferred income tax assets 286,495 247,791 Deferred income tax liabilities: Inventory (558) — Prepaid expenses (10,470) (8,514) Property, plant and equipment (98,637) (82,539) Other (2,458) (2,441) Total deferred income tax liabilities (112,123) (93,494) Net deferred income tax asset $ 174,372 $ 154,297 The Company has federal net operating loss ("NOL") carryforwards of approximately $920.7 million as of December 31, 2020, of which $27.8 million are indefinite lived and the remainder expire predominantly in December 31, 2034 through December 31, 2036. The Company has state NOL carryforwards of approximately $995.8 million, of which $27.8 million are indefinite lived and the remainder expire predominantly in December 31, 2029 through December 31, 2031. The increase in the federal and state NOLs from the prior year was primarily driven by the Company applying a 100%, first-year bonus depreciation for certain qualified equipment for tax purposes as allowed under the Tax Cuts and Jobs Act combined with the current year net loss. In addition, the Company has approximately $18.6 million of general business credits which begin to expire in December 31, 2027 and fully expire in December 31, 2040. The increase in the general business credits from the prior year is due to a $4.0 million income tax benefit from the Internal Revenue Code ("IRC") Section 451 Marginal Well Credit. The Marginal Well Credit is a production-based tax credit that provides a credit for qualified natural gas production. The credit is phased out when natural gas prices exceed certain levels. Under the IRC of 1986, as amended (the "Code"), a company is generally allowed a deduction for NOLs against its federal taxable income. A company’s ability to deduct its NOLs and utilize certain other available tax attributes can be substantially constrained under the general annual limitation rules of Section 382 of the Code if it undergoes an “ownership change” as defined in Section 382 or if similar provisions of state law apply. While the Company does not believe an ownership change has occurred since April 1, 2016, because the rules under Section 382 are highly complex and actions of the Company's stockholders which are beyond its control or knowledge could impact whether an ownership change has occurred, the Company cannot give you any assurance that another Section 382 ownership change has not occurred or will not occur in the future. As a result of the Company qualifying for the aforementioned exception, were the Company to have undergone a subsequent ownership change prior to April 1, 2018, its NOLs would effectively be reduced to zero. An ownership change after such date would severely limit the Company's ability to utilize its NOLs and other tax attributes. Rights Agreement On February 14, 2020, we adopted the Rights Agreement in an effort to prevent the imposition of significant limitations under Section 382 of the Code on our ability to utilize our current NOLs to reduce our future tax liabilities. The Rights Agreement is intended to supplement the 382 Transfer Restrictions and is designed to serve the interests of all stockholders by preserving the availability of our NOLs and is similar to plans adopted by other companies with significant NOLs. Pursuant to the Rights Agreement, one preferred stock purchase right (a “Right” or the “Rights”) will be distributed to stockholders of the Company for each share of common stock of the Company outstanding as of the close of business on February 28, 2020. Initially, these Rights will not be exercisable and will trade with the shares of common stock. If the Rights become exercisable, each Right will initially entitle stockholders to buy one one-thousandth of a share of a newly created series of preferred stock designated as “Series A Junior Participating Preferred Stock” at an exercise price of $31.00 per Right. While the Rights Agreement is in effect, any person or group that acquires beneficial ownership of 4.99% or more of the common stock or any existing stockholder who currently owns 5.00% or more of the common stock that acquires any additional shares of common stock (such person, group or existing stockholder, an "Acquiring Person") without approval from the Board would be subject to significant dilution in their ownership interest in the Company. In such an event, each Right will entitle its holder to buy, at the exercise price, common stock having a market value of two times the then current exercise price of the Right and the Rights held by such Acquiring Person will become void. The Rights Agreement also gives discretion to the Board to determine that someone is an Acquiring Person even if they do not own 4.99% or more of the common stock but do own 4.99% or more in value of the outstanding stock, as determined pursuant to Section 382 of the Code and the regulations promulgated thereunder. In addition, the Board has established procedures to consider requests to exempt certain acquisitions of the Company’s securities from the Rights Agreement if the Board determines that doing so would not limit or impair the availability of the NOLs or is otherwise in the best interests of the Company. The Board may redeem the Rights for $0.01 per Right at any time before any person or group triggers the Rights Agreement. The distribution of the Rights is not a taxable event for stockholders of the Company and will not affect the Company’s’ financial condition or results of operations (including earnings per share). The Rights will expire on the earliest of (i) the close of business on February 14, 2023,(ii) the close of business on the first anniversary of the date of entry into the Rights Agreement, if stockholder approval of the Rights Agreement has not been received by or on such date, (iii) the time at which the Rights are redeemed as provided in the Rights Agreement, (iv) the time at which the Rights are exchanged as provided in the Rights Agreement, (v) the time at which the Board determines that the NOLs are fully utilized or no longer available under Section 382 of the Code, (vi) the effective date of the repeal of Section 382 of the Code if the Board determines that the Rights Agreement is no longer necessary or desirable for the preservation of NOLs, or (vii) the closing of any merger or other acquisition transaction involving the Company pursuant to an agreement of the type described in the Rights Agreement. Valuation Allowance The Company periodically assesses whether it is more likely than not that it will generate sufficient taxable income to realize its deferred income tax assets. The Company establishes valuation allowances if it is not likely it will realize its deferred income tax assets. In making this determination, the Company considers all available positive and negative evidence and makes certain assumptions. The Company considers, among other things, all available positive and negative evidence, including scheduled reversals of deferred tax liabilities, projected future taxable income, the overall business environment, its historical financial results, the industry's historically cyclical financial results, its cumulative three-year income or loss position and potential current and future tax planning strategies. At December 31, 2017, the Company had a valuation allowance established against its deferred income tax assets, which represented a full valuation allowance against its net deferred income tax assets. As of December 31, 2018, after considering all relevant factors, the Company concluded that its deferred income tax assets were more likely than not to be realized and released its valuation allowance against its net deferred income tax assets resulting in a $225.8 million income tax benefit. As of December 31, 2020, the Company considered all positive and negative evidence and concluded that our deferred income tax assets remain more likely than not to be realized and a valuation allowance was not required. Certain factors, could change or circumstances could arise that could further limit or eliminate the amount of the available NOLs to the Company, such as an ownership change or an adjustment by a tax authority. Also, certain circumstances, such as the COVID-19 pandemic and the unknown duration and overall impact on our operations, including our failing to generate sufficient future taxable income from operations, could limit our ability to fully utilize our deferred tax assets before expiration. The following table shows the balance of our valuation allowance and the associated activity during 2018: December 31, 2018 Beginning balance $ 312,493 Addition/(Reduction) - current tax expense/(benefit) (86,679) Release $ (225,814) Ending balance $ — Uncertain Tax Positions The Company has filed income tax returns in the U.S. and in various state and local jurisdictions which are routinely examined by tax authorities in these jurisdictions. NOLs and carryforwards are subject to adjustments based on examination and the statute of limitations is currently open for all such loss and credit carryforwards. The Company had no unrecognized tax benefits or accruals for unrecognized tax benefits as of December 31, 2020 and 2019, respectively.

Asset Retirement Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2020
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations	Asset Retirement ObligationsChanges in the asset retirement obligations (“ARO”) were as follows (in thousands): December 31, 2020 December 31, 2019 Balance at Beginning of Period $ 56,206 $ 61,824 Accretion expense 3,004 3,169 Revisions to estimates 2,973 (7,825) Obligations settled (276) (962) Balance at End of Period $ 61,907 $ 56,206 The portion of costs expected to be paid within a year as of December 31, 2020 is $4.4 million. The portion of costs expected to be incurred beyond one year as of December 31, 2020 is $57.6 million. There were no assets that were legally restricted for purposes of settling asset retirement obligations at December 31, 2020. Alabama's regulatory framework technically allows for self-bonding. However, as a practical matter, due to the onerous regulatory requirements for self-bonding, mining companies in Alabama utilize surety bonds, collateral bonds, or letters of credit to meet their financial assurance requirements. At December 31, 2020, the Company had outstanding surety bonds and letters of credit with parties for post-mining reclamation at all of its mining operations totaling $40.8 million, and $3.6 million for miscellaneous purposes. For the year ended December 31, 2020 and December 31, 2019, the change to the liability was primarily attributable to the net impact of changes in discount rates and current estimates of the costs and scope of remaining reclamation work. For the years ended December 31, 2020 and December 31, 2019, $0.4 million or $0.01 per share and $11.1 million or $0.22 per share, respectively, of the adjustment to the liability was reflected as income in the period because there was no asset recorded to offset the adjustment to the respective liability. This portion of the liability relates to operations that were idle at the time of purchase accounting for the acquisition of certain assets of Walter Energy and no value was attributed to any asset as an offset for the asset retirement obligation.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2020
Payables and Accruals [Abstract]
Accrued Expenses	Accrued Expenses Accrued expenses consisted of the following (in thousands): December 31, 2020 December 31, 2019 Accrued wages and employee benefits $ 25,539 $ 38,680 Accrued operating expenses 46,285 14,014 Accrued royalties 3,484 3,304 Accrued freight 2,724 1,971 Accrued interest 4,981 4,635 Accrued non-income taxes 3,095 3,151 Total accrued expenses $ 86,108 $ 65,755

Pneumoconiosis ("Black Lung") O

Pneumoconiosis ("Black Lung") Obligations	12 Months Ended
	Dec. 31, 2020
Self Insurance Reserve Disclosure [Abstract]
Pneumoconiosis (Black Lung) Obligations	Pneumoconiosis ("Black Lung") Obligations The Company is responsible for medical and disability benefits for black lung disease under the Federal Coal Mine Health and Safety Act of 1969, as amended. Beginning on April 1, 2016 through May 31, 2018, the Company was insured under a guaranteed cost insurance policy, through a third-party insurance carrier, for black lung claims raised by any employee subsequent to the acquisition of certain assets of Walter Energy. Beginning on June 1, 2018 through May 31, 2020, the Company had a deductible policy where the Company is responsible for the first $0.5 million for each black lung claim. Since June 1, 2020, the Company has a deductible policy where the Company is responsible for the first $1.0 million for each black lung claim. In addition, in connection with the acquisition of certain assets of Walter Energy, the Company assumed all black lung liabilities of Walter Energy and its U.S. subsidiaries incurred prior to March 31, 2016, for which the Company is self-insured. Due to a limited operating history as a stand-alone company and as a result of being self-insured for these historical black lung claims, the Department of Labor required the Company to post $17.0 million in the form of Treasury bills or surety bonds as collateral, in addition to maintaining a black lung trust acquired in the Walter Energy acquisition. We received a letter from the Department of Labor on February 21, 2020 under its new process for self-insurance renewals that would require us to increase

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2020
Retirement Benefits [Abstract]
Employee Benefit Plans	Employee Benefit Plans Defined Contribution Plans The Company sponsors a defined contribution plan to assist its eligible employees in providing for retirements. Generally, under the terms of the plan, employees make voluntary contributions through payroll deductions and the Company makes matching contributions, as defined by the plan. Contributions to these defined contribution plans amounted to $3.0 million for the year ended December 31, 2020, $2.9 million for the year ended December 31, 2019 and $3.1 million for the year ended December 31, 2018 accounted for in cost of sales and selling, general and administrative costs. Collective Bargaining Agreement In connection with the acquisition of certain assets of Walter Energy, the Company negotiated a new initial collective bargaining agreement (“CBA”) with the United Mine Workers of America ("UMWA") (the “UMWA CBA”), which was ratified by UMWA’s members on February 16, 2016 and expires on March 31, 2021. Approximately 67.2% and 68.2% of the Company's employees were represented by the UMWA as of December 31, 2020 and December 31, 2019, respectively.

Equity Award Plans

Equity Award Plans	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Equity Award Plans	Equity Award Plans Warrior Met Coal, LLC 2016 Equity Incentive Plan The Company adopted the Warrior Met Coal, LLC 2016 Equity Incentive Plan (the “2016 Equity Plan”). Under the 2016 Equity Plan, employees, directors and officers of the Company were granted equity interests in Warrior Met Coal, LLC in the form of restricted shares and phantom shares. The restricted shares have certain service-based, performance-based and market-based vesting conditions, including the occurrence of an initial public offering or a change in control as set forth in the 2016 Equity Plan and the applicable award agreements. As of December 31, 2020, 805,083 shares were issued, of which, approximately 30,199 have been forfeited, 722,663 have vested and 52,221 remain unvested. Upon effectiveness of the 2017 Equity Plan (defined below), no further awards were granted under the 2016 Equity Plan. Restricted shares were issued proportionally as Tranche A, Tranche B and Tranche C shares. Tranche B and C shares fully vested in 2017. As of December 31, 2020, 268,352 Tranche A shares were issued, of which, approximately 25,551 have been forfeited, 190,580 have vested and 52,221 remain unvested. The Tranche A shares have service and performance based vesting conditions and the awards vest in equal installments on each of the first five anniversaries of the grant date that occurs prior to an IPO and thereafter, subject to the employee’s continued employment or the director’s continued service with the Company. Vesting is conditioned and contingent upon at least 50% of the shares originally acquired in the acquisition of certain assets of Walter Energy having been disposed of to an independent third party, whether before or after an IPO. In the event of a change in control, any Tranche A shares that have not previously vested shall become fully vested at the time of such change in control, subject to the employee’s continued employment or the director's continued service with the Company through the change in control date. During the second quarter of 2018, certain stockholders of the Company sold in two separate transactions an aggregate of 13,000,000 shares of the Company's common stock in public secondary offerings (see Note 17). In connection with the first of these secondary offerings, the performance based vesting condition was met resulting in approximately $3.6 million of incremental stock compensation expense in 2018. The remaining awards shall vest over the remaining time based vesting conditions. The Company recognized stock compensation expense of $0.3 million for the year ended December 31, 2020 associated with the Tranche A shares. As of December 31, 2020, unrecognized compensation expense related to the 2016 Equity Plan amounted to approximately $0.1 million. Holders of phantom shares have the right to receive shares of the Company on the earlier of (i) a change in control as defined by the 2016 Equity Plan or (ii) the fifth anniversary of the grant date of the phantom share. The phantom shares are settled in the Company’s shares. As of December 31, 2020, there were 43,580 phantom shares issued to a director of the Company, all of which were fully vested upon issuance. Warrior Met Coal, Inc. 2017 Equity Incentive Plan In connection with the Company's initial public offering, the Company adopted the Warrior Met Coal, Inc. 2017 Equity Incentive Plan (the “2017 Equity Plan”). Awards previously issued and outstanding under the 2016 Equity Plan will continue to be governed by the 2016 Equity Plan. However, no further awards will be granted under the 2016 Equity Plan. Under the 2017 Equity Plan, directors, officers, employees, consultants and advisors and those of affiliated companies, as well as those who have accepted offers of employment or consultancy from the Company or the Company’s affiliated companies, may be granted equity interest in Warrior Met Coal, Inc. in the form of stock options, stock appreciation rights, restricted stock, restricted stock units, stock bonus awards, and performance awards. The total number of shares of common stock, including incentive stock options, available for grant of awards under the 2017 Equity Plan as of December 31, 2020 is 4,977,874. If any outstanding award expires, is canceled, forfeited, or settled in cash, the shares allocable to that award will again be available for grant under the 2017 Equity Plan. As of December 31, 2020, the equity awards granted under the 2017 Equity Plan are comprised of common stock, restricted stock awards, and restricted stock unit awards. The Company recognized stock compensation expense of $7.3 million for the year ended December 31, 2020 associated with awards granted under the 2017 Equity Plan. Unrecognized compensation expense related to the 2017 Equity Plan amounted to approximately $3.5 million as of December 31, 2020. A summary of activity related to restricted stock unit award grants under the 2017 Equity Incentive Plan during the year ended December 31, 2020 is as follows: Shares Weighted Average Grant Date Fair Value Non-vested at December 31, 2019 503,892 $ 21.57 Granted 477,703 $ 12.38 Canceled (633) $ 22.21 Forfeited (16,267) $ 18.42 Vested (165,455) $ 26.04 Outstanding at December 31, 2020 799,240

Debt

Debt	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Debt	Debt Debt consisted of the following (in thousands): December 31, 2020 December 31, 2019 Weighted Average Interest Rate at December 31, 2020 Final Maturity Senior secured notes $ 343,435 $ 343,435 8% 2024 ABL facility 40,000 — 4% 2023 Debt discount, net (3,527) (4,246) Total debt 379,908 339,189 Less: current debt — — Total long-term debt $ 379,908 $ 339,189 The Company's minimum debt repayment schedule, excluding interest, as of December 31, 2020 is as follows (in thousands): Payments Due 2020 2021 2022 2023 2024 Thereafter Senior secured notes $ — $ — $ — $ — $ 343,435 $ — ABL facility — — — 40,000 — — Total $ — $ — $ — $ 40,000 $ 343,435 $ — ABL Facility On October 15, 2018, the Company entered into an Amended and Restated Asset-Based Revolving Credit Agreement, by and among the Company and certain of its subsidiaries, as borrowers, the guarantors party thereto, the lenders from time to time party thereto and Citibank, N.A, as administrative agent and collateral agent (in such capacities, the "Agent"), which amended and restated in its entirety the existing ABL Facility, and, among other things (i) increased the aggregate commitments available to be borrowed under the ABL Facility to $125.0 million, (ii) extended the maturity date of the ABL Facility to October 15, 2023, (iii) decreased the applicable interest rate margins with respect to the loans and the applicable fees in connection with the issuance of letters of credit, and (iv) amended certain covenants and other terms and provisions. On December 19, 2019, the Company entered into an Amendment No. 2 to the Amended and Restated Credit Agreement (the “Second Amendment”), which, among other things, amended the definitions of Fixed Charges and Fixed Charge Coverage Ratio in the Amended and Restated Credit Agreement to generally conform to the corresponding definitions in the Indenture (as defined below), solely for purposes of incurring unsecured debt based upon the Fixed Charge Coverage Ratio and added customary language in connections with the Qualified Financial Contract Stay Rules. On July 20, 2020, we entered into an Amendment No. 3 to the Amended and Restated Credit Agreement (the "Third Amendment"), which among other things (i) clarified certain definitions related to the calculation of the borrowing base and (ii) decreased the aggregate commitments available to be borrowed under the ABL Facility to $120.0 million on February 28, 2021. Under the ABL Facility, up to $10.0 million of the commitments may be used to incur swingline loans from Citibank and up to $50.0 million of the commitments may be used to issue letters of credit. The ABL Facility will mature on October 15, 2023. As of December 31, 2020, the Company had an aggregate principal amount of $40.0 million drawn under the ABL Facility and there were $9.4 million of letters of credit issued and outstanding under the ABL Facility. At December 31, 2020, the Company had $31.6 million of availability under the ABL Facility. The ABL Facility contains customary covenants for asset-based credit agreements of this type, including among other things: (i) requirements to deliver financial statements, other reports and notices; (ii) restrictions on the existence or incurrence of certain indebtedness; (iii) restrictions on the existence or incurrence of certain liens; (iv) restrictions on making certain restricted payments; (v) restrictions on making certain investments; (vi) restrictions on certain mergers, consolidations and asset dispositions; (vii) restrictions on certain transactions with affiliates; and (viii) restrictions on modifications to certain indebtedness. Additionally, the ABL Facility contains a springing fixed charge coverage ratio of not less than 1.00 to 1.00, which ratio is tested if availability under the ABL Facility is less than a certain amount. As of December 31, 2020, the Company was not subject to this covenant. Subject to customary grace periods and notice requirements, the ABL Facility also contains customary events of default. The Company was in compliance with all applicable covenants under the ABL Facility as of December 31, 2020. Senior Secured Notes On November 2, 2017, the Company consummated a private offering (the “Offering”) of $350.0 million aggregate principal amount of 8.00% Senior Secured Notes due 2024 to qualified institutional buyers pursuant to Rule 144A under the Securities Act of 1933, as amended (the “Securities Act”), and to certain non-U.S. persons in transactions outside the United States in accordance with Regulation S under the Securities Act. The Company used the net proceeds of approximately $340.0 million from the Offering, together with cash on hand of approximately $260.0 million, to pay a special cash dividend of approximately $600.0 million, or $11.21 per share, to all of its stockholders on a pro rata basis (the "November Special Dividend"). On March 1, 2018, the Company issued $125.0 million in aggregate principal amount of its 8.00% Senior Secured Notes due 2024 (the "New Notes") to qualified institutional buyers pursuant to Rule 144A under the Securities Act of 1933, as amended (the "Securities Act"), and to certain non-U.S. persons in transactions outside the United States in accordance with Regulation S under the Securities Act ("Regulation S"). The New Notes were issued at 103.00% of the aggregate principal amount thereof, plus accrued interest from November 2, 2017. The New Notes were issued as "Additional Notes" under the indenture dated as of November 2, 2017 (the "Original Indenture") among the Company, the subsidiary guarantors party thereto and Wilmington Trust, National Association, as trustee (the "Trustee") and priority lien collateral trustee (the "Priority Lien Collateral Trustee"), as supplemented by the First Supplemental Indenture, dated as of March 1, 2018 (the "First Supplemental Indenture" and, the Original Indenture as supplemented thereby, the "Indenture"). The New Notes have not been and will not be registered under the Securities Act, and may not be offered or sold in the United States absent registration or an applicable exemption from the registration requirements of the Securities Act. The Company used the net proceeds of the offering of the New Notes, together with cash on hand of $225.0 million, to pay a special dividend of approximately $350.0 million, or $6.53 per share, to all of its stockholders on a pro rata basis on April 20, 2018 (the "April Special Dividend"). In connection with the issuance of the New Notes, the Company incurred transaction costs of $6.4 million for the year ended December 31, 2018, which consists of legal fees and structuring fees, and is included in transaction and other expenses in the Statements of Operations. In addition, the Company incurred debt issuance costs of approximately $3.7 million, which consists of consent solicitation fees paid to holders of the Existing Notes (as defined below), and is included in long-term debt in the Balance Sheet. The New Notes and the $350.0 million in aggregate principal amount of the Company’s existing 8.00% Senior Secured Notes due 2024 (the “Existing Notes” and, together with the New Notes, the "Notes"), rank pari passu in right of payment and constitute a single class of securities for all purposes under the Indenture, including, without limitation, waivers, amendments, redemptions, offers to purchase and collateral matters, and are fungible (except that the New Notes issued pursuant to Regulation S traded separately under different CUSIP/ISIN numbers until 40 days after the issue date, but thereafter any such holders may transfer their New Notes pursuant to Regulation S into the same CUSIP/ISIN numbers as the Existing Notes issued pursuant to Regulation S). The Notes will mature on November 1, 2024 and interest is payable on May 1 and November 1 of each year, commencing May 1, 2018. The Notes are fully and unconditionally guaranteed on a joint and several basis by each of the Company's direct and indirect wholly-owned domestic restricted subsidiaries that are guarantors under the ABL Facility (subject to customary release provisions). The Notes are redeemable at the Company's option, in whole or in part, from time to time, on or after November 1, 2020, at redemption prices specified in the indenture, plus accrued and unpaid interest, if any, to, but excluding the redemption date. The Company is also required to make offers to purchase the Notes (i) at a purchase price of 101.00% of the principal amount thereof in the event it experiences specific kinds of change of control triggering events, (ii) at a purchase price of 103.00% of the principal amount thereof prior to making certain restricted payments, and (iii) at a purchase price of 100.00% of the principal amount thereof in the event it makes certain asset sales or dispositions and does not reinvest the net proceeds therefrom or use such net proceeds to repay certain indebtedness, in each case, plus accrued and unpaid interest, if any, to, but excluding the date of purchase. Offer to Purchase the Notes On February 21, 2019, the Company commenced an offer to purchase (the “Restricted Payment Offer”), in cash, up to $150,000,000 principal amount of its outstanding Notes, at a repurchase price of 103% of the aggregate principal amount of such Notes, plus accrued and unpaid interest with respect to such Notes to, but not including, the date of repurchase (the “Restricted Payment Repurchase Price”). Concurrently with, but separate from, the Restricted Payment Offer, the Company commenced a cash tender offer (the “Tender Offer” and, together with the Restricted Payment Offer, the “Offers”) to purchase up to $150,000,000 principal amount of the Notes at a repurchase price of 104.25% of the aggregate principal amount of such Notes, plus accrued and unpaid interest to, but not including, the date of repurchase (the “TO Repurchase Price”). The Offers expired on March 22, 2019 (the “Expiration Date”). Restricted Payment Offer As of the Expiration Date, $1,900,000 aggregate principal amount of the Notes were validly tendered and not validly withdrawn pursuant to the Restricted Payment Offer. Pursuant to the terms of the Restricted Payment Offer: (1) an automatic pro ration factor of 31.5789% was applied to the $1,900,000 aggregate principal amount of the Notes that were validly tendered and not validly withdrawn in the Restricted Payment Offer (rounded down to avoid the purchase of Notes in a principal amount other than in integrals of $1,000), which resulted in $599,000 aggregate principal amount of the Notes (the “RP Pro-Rated Tendered Notes”); (2) the Company accepted all $599,000 aggregate principal amount of the RP Pro-Rated Tendered Notes for payment of the Restricted Payment Repurchase Price in cash; and (3) the remaining balance of $1,301,000 aggregate principal amount of the Notes tendered that were not RP Pro-Rated Tendered Notes were not accepted for payment and were returned to the tendering holder of the Notes. The Company consummated the Restricted Payment Offer on March 25, 2019. Accordingly, pursuant to the terms of the Indenture, the Company was permitted to make one or more restricted payments in the form of special dividends to holders of the Company’s common stock and/or repurchases of the Company’s common stock in the aggregate amount of up to $299,401,000 (the "RP Basket") without having to make another offer to repurchase Notes. The Company used a portion of the RP Basket to pay the April 2019 Special Dividend (as defined below) and intends to use the remainder of the RP Basket to make repurchases under the New Stock Repurchase Program (as defined below). Tender Offer As of the Expiration Date, $415,099,000 aggregate principal amount of the Notes were validly tendered and not validly withdrawn pursuant to the Tender Offer. Pursuant to the terms of the Tender Offer: (1) an automatic pro ration factor of 31.5789% was applied to the $415,099,000 aggregate principal amount of the Notes that were validly tendered and not validly withdrawn in the Tender Offer (rounded down to avoid the purchase of Notes in a principal amount other than in integrals of $1,000), which resulted in $130,966,000 aggregate principal amount of the Notes (the “TO Pro-Rated Tendered Notes”); (2) the Company accepted all $130,966,000 aggregate principal amount of the TO Pro-Rated Tendered Notes for payment of the TO Repurchase Price in cash; and (3) the remaining balance of $284,133,000 aggregate principal amount of the Notes tendered that were not TO Pro-Rated Tendered Notes were not accepted for payment and were returned to the tendering holder of the Notes. The Company consummated the Tender Offer on March 26, 2019. In connection with the payments for the RP Pro-Rated Tendered Notes and the TO Pro-Rated Tendered Notes, the Company recognized a loss on early extinguishment of debt of $9.8 million during the year ended December 31, 2019.

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	Leases The Company primarily enters into rental agreements for certain mining equipment that are for periods of 12 months or less, some of which include options to extend the leases. Leases that are for periods of 12 months or less are not recorded on the balance sheet in accordance with the Company's accounting policy election described in Note 2. The Company recognizes lease expense on these agreements on a straight-line basis over the lease term. Additionally, the Company has certain finance leases for mining equipment that expire over various contractual periods. These leases have remaining lease terms of one Supplemental balance sheet information related to leases was as follows (in thousands): December 31, 2020 December 31, 2019 Finance lease right-of-use assets, net (1) $ 46,746 $ 40,227 Finance lease liabilities Current 14,385 10,146 Noncurrent 24,091 25,528 Total finance lease liabilities $ 38,476 $ 35,674 Weighted average remaining lease term - finance leases (in months) 42.9 44.7 Weighted average discount rate - finance leases (2) 5.77 % 6.02 % (1) Finance lease right-of-use assets, recorded net of accumulated amortization of $9.8 million and $4.8 million, are included in property, plant and equipment, net in the Balance Sheets as of December 31, 2020 and December 31, 2019, respectively. See Note 5 for additional disclosure. (2) When an implicit discount rate is not readily available in a lease, the Company uses its incremental borrowing rate based on information available at the commencement date when determining the present value of lease payments. The components of lease expense were as follows (in thousands): For the year ended December 31, 2020 2019 Operating lease cost (1): $ 2,980 $ 2,527 Finance lease cost: Amortization of leased assets 12,730 11,202 Interest on lease liabilities 1,988 1,761 Net lease cost $ 17,698 $ 15,490 (1) Includes leases that are for periods of 12 months or less. Maturities of lease liabilities were as follows (in thousands): Finance Leases (1) 2021 $ 16,276 2022 12,555 2023 10,774 2024 2,557 2025 732 Thereafter — Total 42,894 Less: amount representing interest (4,418) Present value of lease liabilities $ 38,476 (1) Finance lease payments include $1.6 million of future payments required under signed lease agreements that have not yet commenced. Supplemental cash flow information related to leases was as follows (in thousands): For the year ended December 31, 2020 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from finance leases $ 1,988 $ 1,761 Financing cash flows from finance leases $ 14,237 $ 17,273 Non-cash right-of-use assets obtained in exchange for lease obligations: Finance leases $ 18,967 $ 45,523 As of December 31, 2020 the Company had additional commitments for finance leases, primarily for mining equipment, that have not yet commenced, of $1.6 million. These finance leases will commence during fiscal year 2021 with lease terms between one
Leases	Leases The Company primarily enters into rental agreements for certain mining equipment that are for periods of 12 months or less, some of which include options to extend the leases. Leases that are for periods of 12 months or less are not recorded on the balance sheet in accordance with the Company's accounting policy election described in Note 2. The Company recognizes lease expense on these agreements on a straight-line basis over the lease term. Additionally, the Company has certain finance leases for mining equipment that expire over various contractual periods. These leases have remaining lease terms of one Supplemental balance sheet information related to leases was as follows (in thousands): December 31, 2020 December 31, 2019 Finance lease right-of-use assets, net (1) $ 46,746 $ 40,227 Finance lease liabilities Current 14,385 10,146 Noncurrent 24,091 25,528 Total finance lease liabilities $ 38,476 $ 35,674 Weighted average remaining lease term - finance leases (in months) 42.9 44.7 Weighted average discount rate - finance leases (2) 5.77 % 6.02 % (1) Finance lease right-of-use assets, recorded net of accumulated amortization of $9.8 million and $4.8 million, are included in property, plant and equipment, net in the Balance Sheets as of December 31, 2020 and December 31, 2019, respectively. See Note 5 for additional disclosure. (2) When an implicit discount rate is not readily available in a lease, the Company uses its incremental borrowing rate based on information available at the commencement date when determining the present value of lease payments. The components of lease expense were as follows (in thousands): For the year ended December 31, 2020 2019 Operating lease cost (1): $ 2,980 $ 2,527 Finance lease cost: Amortization of leased assets 12,730 11,202 Interest on lease liabilities 1,988 1,761 Net lease cost $ 17,698 $ 15,490 (1) Includes leases that are for periods of 12 months or less. Maturities of lease liabilities were as follows (in thousands): Finance Leases (1) 2021 $ 16,276 2022 12,555 2023 10,774 2024 2,557 2025 732 Thereafter — Total 42,894 Less: amount representing interest (4,418) Present value of lease liabilities $ 38,476 (1) Finance lease payments include $1.6 million of future payments required under signed lease agreements that have not yet commenced. Supplemental cash flow information related to leases was as follows (in thousands): For the year ended December 31, 2020 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from finance leases $ 1,988 $ 1,761 Financing cash flows from finance leases $ 14,237 $ 17,273 Non-cash right-of-use assets obtained in exchange for lease obligations: Finance leases $ 18,967 $ 45,523 As of December 31, 2020 the Company had additional commitments for finance leases, primarily for mining equipment, that have not yet commenced, of $1.6 million. These finance leases will commence during fiscal year 2021 with lease terms between one

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2020
Related Party Transactions [Abstract]
Related Party Transactions	Related Party TransactionsIn connection with the acquisition of certain assets of Walter Energy, the Company acquired a 50% interest in Black Warrior Methane (“BWM”) and Black Warrior Transmission (“BWT”), which are accounted for under the proportionate consolidation method and equity method, respectively. The Company has granted the rights to produce and sell methane gas from its coal mines to BWM and BWT. The Company’s net investments in, advances to/from and equity in earnings or loss of BWT are not material to the Company. The Company supplied labor to BWM and incurred costs, including property and liability insurance, to support the joint venture. The Company charged the joint venture for such costs on a monthly basis, which were $2.6 million for the year ended December 31, 2020, $1.5 million for the year ended December 31, 2019, $3.2 million for the year ended December 31, 2018.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Environmental Matters The Company is subject to a wide variety of laws and regulations concerning the protection of the environment, both with respect to the construction and operation of its plants, mines and other facilities and with respect to remediating environmental conditions that may exist at its own and other properties. The Company believes that it is in substantial compliance with federal, state and local environmental laws and regulations. The Company accrues for environmental expenses resulting from existing conditions that relate to past operations when the costs are probable and can be reasonably estimated. As of December 31, 2020 and December 31, 2019, there were no accruals for environmental matters other than asset retirement obligations for mine reclamation. Miscellaneous Litigation From time to time, the Company is party to a number of lawsuits arising in the ordinary course of their businesses. The Company records costs relating to these matters when a loss is probable and the amount can be reasonably estimated. The effect of the outcome of these matters on the Company’s future results of operations cannot be predicted with certainty as any such effect depends on future results of operations and the amount and timing of the resolution of such matters. As of December 31, 2020 and December 31, 2019, there were no items accrued for miscellaneous litigation. Walter Canada Settlement Proceeds On July 15, 2015, Walter Energy and certain of its wholly owned U.S. subsidiaries, including Jim Walter Resources, Inc. (“JWR”) filed voluntary petitions for relief under Chapter 11 of Title 11 of the U.S. Bankruptcy Code (the “Chapter 11 Cases”) in the Northern District of Alabama, Southern Division. On December 7, 2015, Walter Energy Canada Holdings, Inc., Walter Canadian Coal Partnership and their Canadian affiliates (collectively “Walter Canada”) applied for and were granted protection under the Companies’ Creditors Arrangement Act (the “CCAA”) pursuant to an Initial Order of the Supreme Court of British Columbia. In connection with the Company’s acquisition of certain core operating assets of Walter Energy, the Company acquired a receivable owed to Walter Energy by Walter Canada for certain shared services provided by Walter Energy to Walter Canada (the “Shared Services Claim”) and a receivable for unpaid interest owed to Walter Energy from Walter Canada in respect of a promissory note (the “Hybrid Debt Claim”). Each of these claims were asserted by the Company in the Walter Canada CCAA proceedings. Walter Energy deemed these receivables to be uncollectable for the year ended December 31, 2015 and the Company did not assign any value to these receivables in acquisition accounting as collectability was deemed remote. In March 2020, the Company received approximately $1.8 million in settlement proceeds for the Shared Services Claim and Hybrid Debt Claim and an additional $1.7 million in the fourth quarter of 2020, which are reflected as other income in the Statements of Operations. These settlement proceeds are in addition to the $22.8 million received in 2019 which are reflected as other income in the Statements of Operations. The collectability of additional amounts, if any, related to the Shared Services Claim and Hybrid Debt Claim depends on the outcome of, and the timing of any resolutions of, the Walter Canada CCAA proceedings and cannot be predicted with certainty. Commitments and Contingencies—Other The Company is party to various transportation and throughput agreements with rail and barge transportation providers and the Alabama State Port Authority. These agreements contain annual minimum tonnage guarantees with respect to coal transported from the mine sites to the Port of Mobile in Alabama, unloading of rail cars or barges, and the loading of vessels. If the Company does not meet its minimum throughput obligations, which are based on annual minimum amounts, it is required to pay the transportation providers or the Alabama State Port Authority a contractually specified amount per metric ton for the difference between the actual throughput and the minimum throughput requirement. At December 31, 2020 and December 31, 2019, the Company had no liability recorded for minimum throughput requirements. Royalty Obligations A substantial amount of the coal that the Company mines is produced from mineral reserves leased from third-party land owners. These leases convey mining rights to the Company in exchange for royalties to be paid to the land owner as either a fixed amount per ton or as a percentage of the sales price. Although coal leases have varying renewal terms and conditions, they generally last for the economic life of the reserves. Coal royalty expense was $49.5 million, $87.3 million, $101.0 million, for the years ended December 31, 2020, December 31, 2019, and December 31, 2018, respectively.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Stockholders' Equity	Stockholders' Equity New Stock Repurchase Program On March 26, 2019, the Board approved the Company's second stock repurchase program (the “New Stock Repurchase Program”) that authorizes repurchases of up to an aggregate of $70.0 million of the Company's outstanding common stock. The Company fully exhausted its previous stock repurchase program (the "First Stock Repurchase Program") of $40.0 million of its outstanding common stock. The New Stock Repurchase Program does not require the Company to repurchase a specific number of shares or have an expiration date. The New Stock Repurchase Program may be suspended or discontinued by the Board at any time without prior notice. Under the New Stock Repurchase Program, the Company may repurchase shares of its common stock from time to time, in amounts, at prices and at such times as the Company deems appropriate, subject to market and industry conditions, share price, regulatory requirements and other considerations as determined from time to time by the Company. The Company’s repurchases may be executed using open market purchases or privately negotiated transactions in accordance with applicable securities laws and regulations, including Rule 10b-18 of the Exchange Act and repurchases may be executed pursuant to Rule 10b5-1 under the Exchange Act. Repurchases will be subject to limitations in the ABL Facility and the Indenture. The Company intends to fund repurchases under the New Stock Repurchase Program from cash on hand and/or other sources of liquidity. During the year ended December 31, 2019, the Company repurchased 500,000 shares for approximately $10.6 million, leaving $58.8 million of share repurchases authorized under the New Stock Repurchase Program. In light of the uncertainties resulting from COVID-19 and as a precautionary measure to preserve liquidity, the Company has temporarily suspended its New Stock Repurchase Program. The Company will continue to monitor its liquidity in light of the COVID-19 pandemic and will consider when to reinstate the program. First Stock Repurchase Program On May 2, 2018, the Board approved the First Stock Repurchase Program that authorized repurchases of up to an aggregate of $40.0 million of the Company's outstanding common stock. During the first quarter of 2019, the Company repurchased the remaining share repurchases authorized under the First Stock Repurchase Program for approximately $1.9 million. Secondary Equity Offerings On May 10, 2018 certain stockholders of the Company sold 8,000,000 shares of the Company's common stock in a public secondary offering at a price to the underwriter of $24.20 per share. The Company did not receive any of the proceeds from this offering. In connection with this offering, the Company repurchased 500,000 shares of common stock under the First Stock Repurchase Program, funded with cash on hand for the aggregate amount of $12.1 million (the "Stock Repurchase"). The shares repurchased by the Company in the Stock Repurchase are reflected as Treasury Stock on the Balance Sheets. On June 14, 2018, certain stockholders of the Company sold 5,000,000 shares of the Company's common stock in a public secondary offering at a price to the underwriter of $28.35 per share. The Company did not receive any of the proceeds from the offering. On August 8, 2018, certain stockholders of the Company sold 2,204,806 shares of the Company's common stock in a public secondary offering at a price to the underwriter of $25.40 per share. The Company did not receive any of the proceeds from the offering.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company has no significant assets or other liabilities measured at fair value on a recurring basis as of December 31, 2020 or December 31, 2019. During the year ended December 31, 2020, there were no transfers between Level 1, Level 2 and Level 3. The Company uses quoted dealer prices for similar contracts in active over-the-counter markets for determining fair value of Level 2 liabilities. The following methods and assumptions were used to estimate the fair value for which the fair value option was not elected: Cash and cash equivalents, short-term investments, restricted cash, receivables and accounts payable— The carrying amounts reported in the Balance Sheet approximate fair value due to the short-term nature of these assets and liabilities. Debt— The Company's outstanding debt is carried at cost. As of December 31, 2020, the Company had $40.0 million outstanding under the ABL Facility, with $31.6 million available, net of $9.4 million of letters of credit issued and outstanding at such time. The estimated fair value of the Notes is approximately $352.5 million based upon observable market data (Level 2) and the carrying amount of the ABL Facility approximates fair value as these securities are not traded.

Net (Loss) Income per Share

Net (Loss) Income per Share	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Net (Loss) Income per Share	Net (Loss) Income per Share The computation of basic net (loss) income per share is based on the number of weighted average common shares outstanding during the period. The computation of diluted net (loss) income per share is based on the weighted average number of shares outstanding plus the incremental shares that would be outstanding assuming issuance of restricted stock. The number of incremental shares is calculated by applying the treasury stock method. Basic and diluted net (loss) income per share was calculated as follows (in thousands, except per share data): For the years ended December 31, 2020 2019 2018 Numerator: Net (loss) income $ (35,761) $ 301,699 $ 696,787 Denominator: Weighted-average shares used to compute net (loss) income per share—basic 51,168 51,363 52,812 Dilutive restricted stock awards and units (1) — 130 106 Weighted-average shares used to compute net (loss) income per share—diluted 51,168 51,493 52,918 Net (loss) income per share—basic $ (0.70) $ 5.87 $ 13.19 Net (loss) income per share—diluted $ (0.70) $ 5.86 $ 13.17 (1) In periods of net loss, the number of shares used to calculate diluted earnings per share is the same as basic earnings per share; therefore, the effect of dilutive securities is zero for such periods. As of December 31, 2020, there were 281,588 restricted stock unit awards for which the service-based vesting conditions for these awards were not met as of the measurement date. As such, these awards were excluded from basic earnings per share. As of December 31, 2020, there were 447,295 shares granted under the 2017 Equity Plan to employees, for which neither the service based nor performance based vesting conditions were met as of the measurement date. As such, these shares have been excluded from basic and diluted earnings per share. As of December 31, 2020, there were 52,221 shares of common stock issued under the 2016 Equity Plan to certain directors and employees, for which the service based vesting conditions were not met as of the measurement date. As such, these awards were excluded from basic earnings per share. As of December 31, 2020, there were 43,580 shares of common stock contingently issuable upon the settlement of a vested phantom unit award under the 2016 Equity Plan and 13,157 shares of common stock contingently issuable upon the settlement of a vested restricted stock unit award under the 2017 Equity Plan. The settlement date is the earlier of a change in control as described in the 2016 Equity Plan and 2017 Equity Plan or five years from the grant date. These awards are vested and as such have been included in the weighted-average shares used to compute basic and diluted net (loss) income per share. Dividends On May 17, 2017, the Board adopted the Dividend Policy of paying a quarterly cash dividend of $0.05 per share. The Dividend Policy also states the following: In addition to the regular quarterly dividend and to the extent that the Company generates excess cash that is beyond the then current requirements of the business, the Board may consider returning all or a portion of such excess cash to stockholders through a special dividend or implementation of a stock repurchase program. Any future dividends or stock repurchases will be at the discretion of the Board and subject to consideration of a number of factors, including business and market conditions, future financial performance and other strategic investment opportunities. The Company will also seek to optimize its capital structure to improve returns to stockholders while allowing flexibility for the Company to pursue very selective strategic growth opportunities that can provide compelling stockholder returns. The Company has paid a regular quarterly cash dividend of $0.05 per share every quarter since the Board adopted the Dividend Policy. As of December 31, 2020, the Company has paid $39.5 million of regular quarterly cash dividends under the Dividend Policy. On April 3, 2018, the Board declared the April Special Dividend of approximately $350.0 million, which was funded with the net proceeds from the offering of the New Notes due 2024, together with cash on hand of approximately $225.0 million, and was paid on April 20, 2018 to stockholders of record as of the close of business on April 13, 2018. On April 23, 2019, the Board declared a special cash dividend of $4.41 per share (the "April 2019 Special Dividend"), totaling approximately $230.0 million, which was paid on May 14, 2019 to stockholders of record as of the close of business on May 6, 2019.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Segment Information	Segment Information The Company identifies a business as an operating segment if: i) it engages in business activities from which it may earn revenues and incur expenses; ii) its operating results are regularly reviewed by the Chief Operating Decision Maker (“CODM”), who is the Company’s Chief Executive Officer, to make decisions about resources to be allocated to the segment and assess its performance; and iii) it has available discrete financial information. The Company has determined that its two underground mining operations are its operating segments. The CODM reviews financial information at the operating segment level to allocate resources and to assess the operating results and financial performance for each operating segment. Operating segments are aggregated into a reportable segment if the operating segments have similar quantitative economic characteristics and if the operating segments are similar in the following qualitative characteristics: i) nature of products and services; ii) nature of production processes; iii) type or class of customer for their products and services; iv) methods used to distribute the products or provide services; and v) if applicable, the nature of the regulatory environment. The Company has determined that the two operating segments are similar in both quantitative and qualitative characteristics and thus the two operating segments have been aggregated into one reportable segment. The Company has determined that its natural gas and royalty businesses and other unallocated activities did not meet the criteria in ASC 280 to be considered as operating or reportable segments. Therefore, the Company has included their results in an “all other” category as a reconciling item to consolidated amounts. The Company does not allocate all of its assets, or its depreciation and depletion expense, selling, general and administrative expenses, other post-retirement benefits, transactions costs, restructuring costs, interest expense, reorganization items, net and income tax expense by segment. The following tables include reconciliations of segment information to consolidated amounts (in thousands): For the years ended December 31, 2020 2019 2018 Revenues Mining $ 761,871 $ 1,235,998 $ 1,342,683 All other 20,867 32,311 35,324 Total revenues $ 782,738 $ 1,268,309 $ 1,378,007 For the years ended December 31, 2020 2019 2018 Capital Expenditures Mining $ 78,015 $ 100,768 $ 97,607 All other 9,473 6,510 4,013 Total capital expenditures $ 87,488 $ 107,278 $ 101,620 The Company evaluates the performance of its segment based on Segment Adjusted EBITDA, which is defined as net (loss) income adjusted for other revenues, cost of other revenues, depreciation and depletion, selling, general and administrative, other postretirement benefits, and certain transactions or adjustments that the CODM does not consider for the purposes of making decisions to allocate resources among segments or assessing segment performance. Segment Adjusted EBITDA does not represent and should not be considered as an alternative to cost of sales under GAAP and may not be comparable to other similarly titled measures used by other companies. Below is a reconciliation of Segment Adjusted EBITDA to net (loss) income, which is its most directly comparable financial measure calculated and presented in accordance with GAAP (in thousands): For the years ended December 31, 2020 2019 2018 Segment Adjusted EBITDA $ 136,701 $ 515,253 $ 626,038 Other revenues 20,867 32,311 35,324 Cost of other revenues (33,736) (29,828) (10,172) Depreciation and depletion (118,092) (97,330) (97,209) Selling, general and administrative (32,879) (37,014) (36,626) Transaction and other costs — — (9,068) Loss on early extinguishment of debt — (9,756) — Other income 3,544 22,815 — Interest expense, net (32,310) (29,335) (37,314) Income tax (expense) benefit 20,144 (65,417) 225,814 Net (loss) income $ (35,761) $ 301,699 $ 696,787

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Regular Quarterly Dividend On February 18, 2021, the Board declared a regular quarterly cash dividend of $0.05 per share, totaling $2.6 million, which will be paid on March 8, 2021, to stockholders of record as of the close of business on March 1, 2021. Alabama House Bill On February 12, 2021, the Alabama Governor signed into law Alabama House Bill 170, now Act 2021-1 (“the Act”). The Act makes several changes to the state’s business tax structure. While the Company expects that the Act, in its entirety, will not adversely affect the Company, the Company is closely monitoring whether any provisions of the Act could adversely impact the Company. Among the provisions of the Act, is the repeal of the so-called corporate income tax “throwback rule.” That rule required all sales originating in Alabama and delivered to a jurisdiction where the seller was not subject to tax, to be included in the seller’s Alabama income tax base. Thus, prior to repeal of the throwback rule, the Company had to rely on its Alabama NOL carryforwards to shelter taxes imposed under such throwback rule. As a result of the now repealed throwback rule, effective January 1, 2021, all such sales should now be excluded from Alabama taxable income without the need to utilize Alabama NOLs. If it is determined that as a result of the repeal of the throwback rule it is more likely than not that the Company would not have sufficient taxable income to utilize the Company’s state deferred income tax assets, the Company may be required to establish a valuation allowance against such state deferred income tax assets.

Supplemental Summary Quarterly

Supplemental Summary Quarterly Financial Information (Unaudited)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Supplemental Summary Quarterly Financial Information (Unaudited)	Quarter Ended Fiscal Year 2020 March 31 June 30 September 30 December 31 Total revenues $ 226,720 $ 163,701 $ 180,064 $ 212,253 Gross profit (1) $ 67,645 $ 25,282 $ 21,630 $ 9,275 Operating income (loss) $ 30,497 $ (5,331) $ (14,527) $ (37,778) Net income (loss) (2) $ 21,545 $ (9,161) $ (14,434) $ (33,711) Net income (loss) per share—basic (4) $ 0.42 $ (0.18) $ (0.28) $ (0.66) Net income (loss) per share—diluted (4) $ 0.42 $ (0.18) $ (0.28) $ (0.66) Quarter Ended Fiscal Year 2019 March 31 June 30 September 30 December 31 Total revenues $ 378,290 $ 397,613 $ 287,506 $ 204,901 Gross profit (1) $ 187,917 $ 184,406 $ 89,702 $ 55,713 Operating income $ 156,779 $ 147,945 $ 54,599 $ 24,071 Net income (3) $ 110,447 $ 125,481 $ 45,022 $ 20,751 Net income per share—basic (4) $ 2.14 $ 2.43 $ 0.88 $ 0.41 Net income per share—diluted (4) $ 2.14 $ 2.43 $ 0.87 $ 0.41 (1) Represents total revenues less cost of sales (exclusive of items shown separately below) and cost of other revenues (exclusive of items shown separately below) for each respective period. (2) Net income for the three months ended March 31, 2020 includes proceeds received for the Shared Services Claim and Hybrid Debt Claim of $1.8 million. Net loss for the three months ended December 31, 2020 includes settlement proceeds of $1.7 million related to other Walter Energy claims. (3) Net income for the three months ended March 31, 2019 includes a loss on early extinguishment of debt of $9.8 million. Net income includes proceeds received for the Shared Services Claim and Hybrid Debt Claim of $17.5 million and $5.3 million for the three months ended June 30, 2019 and September 30, 2019, respectively. Net income for the three months ended December 31, 2019 includes a change in ARO due to revisions to estimates of $7.8 million which is discussed further in Note 8. (4) The sum of quarterly amounts may not equal the annual amounts reported due to rounding. In addition, the sum of quarterly EPS amounts may be different than annual amounts as a result of the impact of variations in shares outstanding.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements include the accounts of Warrior Met Coal, Inc and its subsidiaries (the "Company"). All significant intercompany transactions and balances have been eliminated in consolidation.
Use of Estimates	Use of Estimates
Concentrations of Credit Risk and Major Customers	Concentrations of Credit Risk and Major Customers The Company’s principal line of business is mining and marketing met coal to foreign steel producers.
Revenue Recognition	Revenue Recognition Revenue is recognized when performance obligations under the terms of a contract with our customers are satisfied; for all contracts this occurs when control of the promised goods have been transferred to our customers. For coal shipments to domestic customers via rail, control is transferred when the railcar is loaded. For coal shipments to international customers via ocean vessel, control is transferred when the vessel is loaded at the Port of Mobile in Alabama. For natural gas sales, control is transferred when the gas has been transferred to the pipeline. Revenue is disaggregated between coal sales within the Company's mining segment and natural gas sales included in all other revenues, as disclosed in Note 20. Our coal and gas sales generally include up to 45-day payment terms following the transfer of control of the goods to the customer. We typically do not include extended payment terms in our contracts with customers.
Trade Accounts Receivable and Allowance for Credit Losses	Trade Accounts Receivable and Allowance for Credit Losses Trade accounts receivable represent customer obligations that are derived from revenue recognized from contracts with customers. Credit is extended based on an evaluation of the individual customer's financial condition. The Company maintains trade credit insurance on the majority of its customers and the geographic regions of coal shipments to these customers. In some instances, the Company requires letters of credit, cash collateral or prepayments from its customers on or before shipment to mitigate the risk of loss. These efforts have consistently resulted in the Company recognizing no historical credit losses. The Company also has never had to have a claim against its trade credit insurance policy. In order to estimate the allowance for credit losses on trade accounts receivable, the Company utilizes an aging approach in which potential impairment is calculated based on how long a receivable has been outstanding (e.g., current, 1-31, 31-60, etc.). The Company calculates an expected credit loss rate based on the Company’s historical credit loss rate, the risk characteristics of our customers, and the current metallurgical coal and steel market environments. As of December 31, 2020, the estimated allowance for credit losses was immaterial and did not have a material impact on the Company's financial statements.
Shipping and Handling	Shipping and Handling Costs incurred to transport coal to the point of sale at the Port of Mobile, Alabama, are included in cost of sales and the gross amounts billed to customers, if any, to cover shipping and handling to the ultimate/final destination are included in sales.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents include short-term deposits and highly liquid investments that have original maturities of three months or less when purchased and are stated at cost, which approximates fair value.
Short-Term Investments	Short-Term Investments Instruments with maturities greater than three months, but less than twelve months, are included in short-term investments. The Company purchases United States Treasury bills with maturities ranging from six to twelve months which are classified as held to maturity and are carried at amortized cost, which approximates fair value. The Company also purchases fixed income securities and certificates of deposits with varying maturities that are classified as available for sale and are carried at fair value. Securities classified as held to maturity securities are those securities that management has the intent and ability to hold to maturity.
Inventories	Inventories Inventories are valued at the lower of cost or net realizable value. Coal inventory costs include labor, supplies, equipment costs, operating overhead, freight, royalties, depreciation and depletion and other related costs. Coal inventories are valued using the first-in, first-out (“FIFO”) inventory valuation method. The valuation of coal inventories is subject to estimates due to possible gains and losses resulting from inventory movements from the mine site to storage facilities, inherent inaccuracies in belt scales and aerial surveys used to measure quantities and fluctuations in moisture content. Periodic adjustments to coal tonnages on hand are made for an estimate of coal shortages and overages due to these inherent gains and losses, primarily based on historical results from aerial surveys and periodic coal pile clean-ups. Supplies inventories are valued using the average cost method of accounting. Management evaluates its supplies inventory in terms of excess and obsolete exposures which includes such factors as anticipated usage, inventory turnover, inventory levels and ultimate market value. A reserve for excess and obsolete supplies inventory is established and charged to cost of sales in the Statements of Operations.
Deferred Longwall Move Expenses and Advanced Mining Royalties	Deferred Longwall Move Expenses Direct costs, including labor and supplies, associated with moving longwall equipment and the related equipment refurbishment costs are deferred and included in prepaid expenses. These deferred costs are amortized on a units-of-production basis into cost of sales over the life of the subsequent panel of coal mined by the longwall equipment. See Note 4 for further disclosures related to deferred longwall move expenses. Advanced Mining Royalties Lease rights to coal reserves are often acquired in exchange for royalty payments. Advance mining royalties are advance payments made to lessors under terms of mineral lease agreements that are recoupable against future production royalties. These advance payments are deferred and charged to operations as the coal reserves are mined. Advance mining royalties are included in other long-term assets.
Property, Plant and Equipment	Property, Plant and Equipment Property, Plant and Equipment Property, plant and equipment are recorded at cost. Depreciation is recorded principally on the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized on the straight-line method over the lesser of the useful life of the improvement or the remaining lease term. Estimated useful lives used in computing depreciation expense range from three fifteen Deferred Mine Development Costs of developing new underground mines and certain underground expansion projects are capitalized. Underground development costs, which are costs incurred to make the coal physically accessible, may include construction permits and licenses, mine design, construction of access roads, main entries, airshafts, roof protection and other facilities. Mine development costs are amortized primarily on a units-of-production basis over the estimated reserve tons directly benefiting from the capital expenditures. Costs amortized during the production phase of a mine are capitalized into inventory and expensed to cost of sales as the coal is sold. Coal sales revenue related to incidental production during the development phase are recorded as sales with an offset to cost of sales based on the estimated cost per ton sold for the mine when the asset is in place for its intended use. Owned and Leased Mineral Interests Costs to obtain coal reserves and lease mineral rights are capitalized based on cost or the fair value at acquisition and depleted using the units-of-production method over the life of proven and probable reserves. Lease agreements are generally long-term in nature (original terms range from 10 to 50 years) and substantially all of the leases contain provisions that allow for automatic extension of the lease term provided certain requirements are met. Depletion expense was $9.3 million, $9.9 million, and $9.6 million for the years ended December 31, 2020, December 31, 2019, and December 31, 2018, respectively, and is included in depreciation and depletion in the accompanying Statements of Operations. Asset Retirement Obligations The Company has certain asset retirement obligations primarily related to mine closing reclamation costs, perpetual water care costs and other costs associated with dismantling and removing facilities. Asset retirement obligations are determined for each mine using various estimates and assumptions, including estimates of disturbed acreage as determined from engineering data, estimates of future costs to reclaim the disturbed acreage and the timing of related cash flows, discounted using a credit-adjusted, risk-free rate. The Company's asset retirement obligations also include estimates to reclaim gas wells in accordance with the Oil and Gas Board of Alabama. On at least an annual basis, the Company reviews the entire asset retirement obligation liability and makes necessary adjustments for permit changes, the anticipated timing of mine closures, and revisions to cost estimates and productivity assumptions to reflect current experience. As changes in estimates occur, the carrying amount of the obligation and asset are revised to reflect the new estimate after applying the appropriate credit-adjusted, risk-free discount rate. The future costs of these obligations are accrued at the estimated fair value in the period in which they are incurred if a reasonable estimate of fair value can be made. The present value of the estimated asset retirement cost is capitalized as part of the carrying amount of the long-lived asset. For sites where there is no asset, expense or income is recognized for changes in estimates. Capitalized asset retirement costs are amortized on a units-of-production basis over the estimated reserves. Accretion of the asset retirement obligation is recognized over time and generally will escalate over the life of the producing asset, typically as production declines. Accretion is included in cost of sales on the Statements of Operations. Accrued mine closing costs, perpetual care costs and reclamation costs and other costs of dismantling and removing facilities are regularly reviewed by management and revised for changes in future estimated costs and regulatory requirements, as necessary. For ongoing operations, adjustments to the liability result in an adjustment to the corresponding asset. For some operations, adjustments to the liability are recognized as income or expense in the period the adjustment is recorded as no asset was recorded to offset the liability established during acquisition accounting related to the acquisition of certain assets of Walter Energy as the operations were idle at that time. Any difference between the recorded obligation and the actual cost of reclamation is recorded in profit or loss in the period the obligation is settled. See Note 8 for further disclosures related to asset retirement obligations. Impairment of Long-Lived Assets Property, plant and equipment and other long-lived assets are reviewed for impairment at least annually or whenever events or changes in circumstances indicate that the book value of the asset may not be recoverable. The Company periodically evaluates whether events and circumstances have occurred that would indicate possible impairment. When impairment indicators exist, the Company uses an estimate of the future undiscounted cash flows of the related asset or asset group over the remaining life in measuring whether or not the asset values are recoverable. If the carrying amount of an asset or asset group exceeds its estimated future cash flows, impairment is recognized equal to the amount by which the carrying amount of the asset exceeds the fair value of the asset or asset group. Fair value is generally determined using market quotes, if available, or a discounted cash flow approach. The Company’s estimate of future undiscounted cash flows is based on assumptions including long-term met coal pricing forecasts, anticipated production volumes and mine operating costs for the life of the mine or estimated useful life of the asset.
Equity Award Compensation (Successor) and Stock-Based Compensation (Predecessor)	Equity Award Compensation The Company accounts for equity award-based compensation to employees and non-employee/directors in accordance with ASC 718 requiring employee equity awards to be accounted for under the fair value method. The Company recognizes forfeitures as they occur. The Company recognizes compensation expense associated with equity awards for all awards made to employees as the requisite service, performance and market vesting conditions are met. For units granted containing only service and performance conditions, the fair value of the award is equal to the market price of the Company's common stock at the date of grant. For units granted containing only a market condition, the fair value of the award is determined utilizing a Monte Carlo simulation model which incorporates the total stockholder return hurdles set for each grant. Compensation expense for equity awards with a service-only condition is recognized over the employee’s requisite service period using a graded vesting method. For awards with a performance condition that affects vesting, the performance condition is not considered in determining the award’s grant-date fair value; however, the performance conditions are considered when estimating the quantity of awards that are expected to vest. No compensation expense is recorded for awards with performance conditions until the performance condition is determined to be probable of achievement. For awards with a market condition that affects vesting, the market condition is considered in determining the award’s grant-date fair value. Compensation expense for awards with a market condition is recognized straight-line over the derived or implied service period. Compensation expense for equity awards is included in cost of sales (exclusive of items shown separately below) and selling, general and administrative in the accompanying Statements of Operations.
Deferred Financing Costs	Deferred Financing Costs The costs to obtain new debt financing or amend existing financing agreements are deferred and amortized to interest expense over the life of the related indebtedness or credit facility using the straight-line method. As of December 31, 2020 and December 31, 2019, there were $2.7 million of unamortized origination fees related to the ABL Facility (as defined in Note 13) in other long-term assets on the accompanying Balance Sheet. As of December 31, 2020 and December 31, 2019 there were $3.5 million and $4.2 million, respectively, of unamortized deferred financing costs and debt discount, net, related to the Notes (as defined in Note 13), which is presented as a net deduction from the carrying amount of the debt recognized in the accompanying Balance Sheet.
Income Taxes	Income TaxesThe Company records a tax provision for the expected tax effects of the reported results of operations. The provision for income taxes is determined using the asset and liability method, under which deferred tax assets and liabilities are recognized for the expected future tax impact of temporary differences between the financial reporting and tax bases of assets and liabilities, and for operating losses and tax credit carryforwards. Deferred income tax assets and liabilities are measured using the currently enacted tax rates that apply to taxable income in effect for the years in which those tax assets and liabilities are expected to be realized or settled. The Company records a valuation allowance to reduce deferred income tax assets to the amount that is believed more likely than not to be realized. When the Company concludes that all or part of the net deferred income tax assets are not realizable in the future, the Company makes an adjustment to the valuation allowance that is charged to earnings in the period that such determination was made.The Company recognizes tax benefits from uncertain tax positions only if it is more likely than not that the tax position will be sustained on examination by the taxing authorities, based on the technical merits of the position. The tax benefits recognized in the financial statements from such positions are then measured based on the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement.
Fair Value Measurements	Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. A three level hierarchy has been established for valuing assets and liabilities based on how transparent (observable) the inputs are that are used to determine fair value, with the inputs considered most observable categorized as Level 1 and those that are the least observable categorized as Level 3. Hierarchy levels are defined as follows: Level 1: Quoted prices in active markets for identical assets and liabilities. Level 2: Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. Level 3: Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.
Leases	LeasesThe Company determines if an arrangement is a lease at inception. The Company has an accounting policy election that leases with an initial term of 12 months or less remain off its balance sheet and lease payments are recognized in the Statements of Operations on a straight-line basis over the lease term. A right-of-use asset represents the Company's right to use an underlying asset for the lease term and lease liabilities represent its obligation to make lease payments arising from the lease. Operating lease right-of-use assets and liabilities are recognized at the lease commencement date based on the present value of the lease payments over the lease term. For purpose of calculating such present values, lease payments include components that vary based on an index or rate, using the prevailing index or rate at the commencement date and exclude components that vary based upon other factors. For those leases that do not contain a readily determinable implicit rate, the Company uses its incremental borrowing rate at commencement to determine the present value of lease payments. Variable lease payments not included within lease contracts are expensed as incurred. The Company's leases may include options to extend or terminate the lease, and such options are reflected in the term when their exercise is reasonably certain. Lease expense is recognized on a straight-line basis over the lease term.
New Accounting Pronouncements	New Accounting Pronouncements The Company adopted Accounting Standards Update ("ASU") 2016-13, "Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments" as of January 1, 2020 using the modified retrospective approach. The ASU requires the use of an “expected loss” model for instruments measured at amortized cost, in which companies will be required to estimate the lifetime expected credit loss and record an allowance to offset the amortized cost basis, resulting in a net presentation of the amount expected to be collected on the financial asset. The adoption of the new standard did not have a material impact on the Company's financial statements, including accounting policies, processes and systems. In December 2019, the Financial Accounting Standards Board ("FASB") issued ASU 2019-12, “Income Taxes (Topic 740) - Simplifying the Accounting for Income Taxes,” which is intended to simplify various aspects related to accounting for income taxes. This ASU removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The ASU is effective for fiscal years beginning after December 15, 2020. The Company expects to adopt the standard as of January 1, 2021 with no material impact to the Company's results of operations, financial condition, cash flows or financial statement presentation.

Inventories, net (Tables)

Inventories, net (Tables)	12 Months Ended
	Dec. 31, 2020
Inventory Disclosure [Abstract]
Schedule of Inventories, Net	Inventories, net are summarized as follows (in thousands): December 31, 2020 December 31, 2019 Coal $ 86,272 $ 69,064 Raw materials, parts, supplies and other, net 32,441 28,837 Total inventories, net $ 118,713 $ 97,901

Prepaid Expenses and Other (Tab

Prepaid Expenses and Other (Tables)	12 Months Ended
	Dec. 31, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Prepaid Expenses	Prepaid expenses and other consisted of the following (in thousands): December 31, 2020 December 31, 2019 Deferred longwall move expenses $ 22,972 $ 15,621 Prepaid insurance 3,832 3,631 Prepaid deposits 6,937 345 Other 6,169 4,247 Total prepaid expenses and other $ 39,910 $ 23,844

Mineral Interests and Propert_2

Mineral Interests and Property, Plant and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Schedule of Property, Plant and Equipment	Property, plant and equipment are summarized as follows (in thousands): December 31, 2020 December 31, 2019 Land $ 71,886 $ 72,267 Land improvements 18,024 18,026 Building and leasehold improvements 77,556 74,342 Mine development and infrastructure costs 29,893 13,315 Machinery and equipment 679,393 614,687 Financing lease right of use asset 56,528 44,996 Construction in progress 82,367 42,106 Total 1,015,647 879,739 Less: Accumulated depreciation (378,539) (273,539) Property, plant and equipment, net $ 637,108 $ 606,200

Other Long-Term Assets (Tables)

Other Long-Term Assets (Tables)	12 Months Ended
	Dec. 31, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Long-Term Assets	Other long-term assets consisted of the following (in thousands): December 31, 2020 December 31, 2019 Advance mining royalties $ 7,305 $ 8,976 ABL Facility origination fees 2,667 2,723 Other 4,146 6,543 Total other long-term assets $ 14,118 $ 18,242

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	Income tax (benefit) expense consisted of the following (in thousands): For the years ended December 31, 2020 2019 2018 Current Federal $ (74) $ (3,151) $ (2,776) State 5 85 — (69) (3,066) (2,776) Deferred Federal (16,731) 53,677 (176,141) State (3,344) 14,806 (46,897) (20,075) 68,483 (223,038) Total $ (20,144) $ 65,417 $ (225,814)
Schedule of Effective Income Tax Rate Reconciliation	Total income tax (benefit) expense differs from the expected tax (benefit) expense (computed by multiplying the U.S. federal statutory rate of 21% by (loss) income before income taxes) as a result of the following (in thousands): For the years ended December 31, 2020 2019 2018 (Loss) income before income tax (benefit) expense $ (55,905) $ 367,116 $ 470,973 Tax (benefit) expense at statutory tax rate (11,740) 77,094 98,904 Effect of: Depletion (1,504) (16,198) (18,227) Tax Cuts and Jobs Act impact — — (2,775) State and local income tax, net of federal effect (2,637) 11,747 14,897 Valuation allowance on deferred tax assets — — (312,493) Non-deductible transaction costs — — 566 Impact of Walter Energy IRS Settlement (1) — (6,615) — IRC Section 451 marginal well credit (3,977) — (4,964) Other (286) (611) (1,722) Tax (benefit) expense recognized $ (20,144) $ 65,417 $ (225,814) (1) In the fourth quarter of 2019, an adjustment of $6.6 million was recorded to recognize additional alternative minimum tax credits, general business credits and NOLs available to the Company in connection with a settlement agreement between Walter Energy and the Internal Revenue Service.
Schedule of Deferred Tax Assets and Liabilities	Significant components of the Company's deferred income tax assets and liabilities were (in thousands): December 31, 2020 December 31, 2019 Deferred income tax assets: Net operating loss and credit carryforwards $ 253,756 $ 215,805 Inventory — 457 Asset retirement obligations 15,547 14,115 Black lung obligations 9,275 8,168 Accrued expenses 4,303 5,597 Other 3,614 3,649 Total deferred income tax assets 286,495 247,791 Deferred income tax liabilities: Inventory (558) — Prepaid expenses (10,470) (8,514) Property, plant and equipment (98,637) (82,539) Other (2,458) (2,441) Total deferred income tax liabilities (112,123) (93,494) Net deferred income tax asset $ 174,372 $ 154,297
Roll Forward of Deferred Tax Asset Valuation Allowance	The following table shows the balance of our valuation allowance and the associated activity during 2018: December 31, 2018 Beginning balance $ 312,493 Addition/(Reduction) - current tax expense/(benefit) (86,679) Release $ (225,814) Ending balance $ —

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2020
Asset Retirement Obligation Disclosure [Abstract]
Schedule of Changes in Asset Retirement Obligations	Changes in the asset retirement obligations (“ARO”) were as follows (in thousands): December 31, 2020 December 31, 2019 Balance at Beginning of Period $ 56,206 $ 61,824 Accretion expense 3,004 3,169 Revisions to estimates 2,973 (7,825) Obligations settled (276) (962) Balance at End of Period $ 61,907 $ 56,206

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2020
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following (in thousands): December 31, 2020 December 31, 2019 Accrued wages and employee benefits $ 25,539 $ 38,680 Accrued operating expenses 46,285 14,014 Accrued royalties 3,484 3,304 Accrued freight 2,724 1,971 Accrued interest 4,981 4,635 Accrued non-income taxes 3,095 3,151 Total accrued expenses $ 86,108 $ 65,755

Equity Award Plans (Tables)

Equity Award Plans (Tables)	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Schedule of Share-based Compensation, Restricted Stock	A summary of activity related to restricted stock unit award grants under the 2017 Equity Incentive Plan during the year ended December 31, 2020 is as follows: Shares Weighted Average Grant Date Fair Value Non-vested at December 31, 2019 503,892 $ 21.57 Granted 477,703 $ 12.38 Canceled (633) $ 22.21 Forfeited (16,267) $ 18.42 Vested (165,455) $ 26.04 Outstanding at December 31, 2020 799,240

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Schedule of Long-Term Debt	Debt consisted of the following (in thousands): December 31, 2020 December 31, 2019 Weighted Average Interest Rate at December 31, 2020 Final Maturity Senior secured notes $ 343,435 $ 343,435 8% 2024 ABL facility 40,000 — 4% 2023 Debt discount, net (3,527) (4,246) Total debt 379,908 339,189 Less: current debt — — Total long-term debt $ 379,908 $ 339,189
Schedule of Maturities of Long-term Debt	The Company's minimum debt repayment schedule, excluding interest, as of December 31, 2020 is as follows (in thousands): Payments Due 2020 2021 2022 2023 2024 Thereafter Senior secured notes $ — $ — $ — $ — $ 343,435 $ — ABL facility — — — 40,000 — — Total $ — $ — $ — $ 40,000 $ 343,435 $ —

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Supplemental balance sheet information	Supplemental balance sheet information related to leases was as follows (in thousands): December 31, 2020 December 31, 2019 Finance lease right-of-use assets, net (1) $ 46,746 $ 40,227 Finance lease liabilities Current 14,385 10,146 Noncurrent 24,091 25,528 Total finance lease liabilities $ 38,476 $ 35,674 Weighted average remaining lease term - finance leases (in months) 42.9 44.7 Weighted average discount rate - finance leases (2) 5.77 % 6.02 % (1) Finance lease right-of-use assets, recorded net of accumulated amortization of $9.8 million and $4.8 million, are included in property, plant and equipment, net in the Balance Sheets as of December 31, 2020 and December 31, 2019, respectively. See Note 5 for additional disclosure.
Direct financing lease, lease income	The components of lease expense were as follows (in thousands): For the year ended December 31, 2020 2019 Operating lease cost (1): $ 2,980 $ 2,527 Finance lease cost: Amortization of leased assets 12,730 11,202 Interest on lease liabilities 1,988 1,761 Net lease cost $ 17,698 $ 15,490 (1) Includes leases that are for periods of 12 months or less.
Operating lease, lease income	The components of lease expense were as follows (in thousands): For the year ended December 31, 2020 2019 Operating lease cost (1): $ 2,980 $ 2,527 Finance lease cost: Amortization of leased assets 12,730 11,202 Interest on lease liabilities 1,988 1,761 Net lease cost $ 17,698 $ 15,490 (1) Includes leases that are for periods of 12 months or less.
Finance lease, liability, maturity	Maturities of lease liabilities were as follows (in thousands): Finance Leases (1) 2021 $ 16,276 2022 12,555 2023 10,774 2024 2,557 2025 732 Thereafter — Total 42,894 Less: amount representing interest (4,418) Present value of lease liabilities $ 38,476 (1) Finance lease payments include $1.6 million of future payments required under signed lease agreements that have not yet commenced.
Supplemental cash flow information	Supplemental cash flow information related to leases was as follows (in thousands): For the year ended December 31, 2020 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from finance leases $ 1,988 $ 1,761 Financing cash flows from finance leases $ 14,237 $ 17,273 Non-cash right-of-use assets obtained in exchange for lease obligations: Finance leases $ 18,967 $ 45,523

Net (Loss) Income per Share (Ta

Net (Loss) Income per Share (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	Basic and diluted net (loss) income per share was calculated as follows (in thousands, except per share data): For the years ended December 31, 2020 2019 2018 Numerator: Net (loss) income $ (35,761) $ 301,699 $ 696,787 Denominator: Weighted-average shares used to compute net (loss) income per share—basic 51,168 51,363 52,812 Dilutive restricted stock awards and units (1) — 130 106 Weighted-average shares used to compute net (loss) income per share—diluted 51,168 51,493 52,918 Net (loss) income per share—basic $ (0.70) $ 5.87 $ 13.19 Net (loss) income per share—diluted $ (0.70) $ 5.86 $ 13.17 (1) In periods of net loss, the number of shares used to calculate diluted earnings per share is the same as basic earnings per share; therefore, the effect of dilutive securities is zero for such periods.

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Reconciliation of Revenue from Segments to Consolidated	The following tables include reconciliations of segment information to consolidated amounts (in thousands): For the years ended December 31, 2020 2019 2018 Revenues Mining $ 761,871 $ 1,235,998 $ 1,342,683 All other 20,867 32,311 35,324 Total revenues $ 782,738 $ 1,268,309 $ 1,378,007
Reconciliation of Capital Expenditures from Segments to Consolidated	For the years ended December 31, 2020 2019 2018 Capital Expenditures Mining $ 78,015 $ 100,768 $ 97,607 All other 9,473 6,510 4,013 Total capital expenditures $ 87,488 $ 107,278 $ 101,620
Reconciliation of Net Income (Loss) from Segments to Consolidated	Below is a reconciliation of Segment Adjusted EBITDA to net (loss) income, which is its most directly comparable financial measure calculated and presented in accordance with GAAP (in thousands): For the years ended December 31, 2020 2019 2018 Segment Adjusted EBITDA $ 136,701 $ 515,253 $ 626,038 Other revenues 20,867 32,311 35,324 Cost of other revenues (33,736) (29,828) (10,172) Depreciation and depletion (118,092) (97,330) (97,209) Selling, general and administrative (32,879) (37,014) (36,626) Transaction and other costs — — (9,068) Loss on early extinguishment of debt — (9,756) — Other income 3,544 22,815 — Interest expense, net (32,310) (29,335) (37,314) Income tax (expense) benefit 20,144 (65,417) 225,814 Net (loss) income $ (35,761) $ 301,699 $ 696,787

Supplemental Summary Quarterl_2

Supplemental Summary Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Supplemental Quarterly Financial Information (Unaudited)	Quarter Ended Fiscal Year 2020 March 31 June 30 September 30 December 31 Total revenues $ 226,720 $ 163,701 $ 180,064 $ 212,253 Gross profit (1) $ 67,645 $ 25,282 $ 21,630 $ 9,275 Operating income (loss) $ 30,497 $ (5,331) $ (14,527) $ (37,778) Net income (loss) (2) $ 21,545 $ (9,161) $ (14,434) $ (33,711) Net income (loss) per share—basic (4) $ 0.42 $ (0.18) $ (0.28) $ (0.66) Net income (loss) per share—diluted (4) $ 0.42 $ (0.18) $ (0.28) $ (0.66) Quarter Ended Fiscal Year 2019 March 31 June 30 September 30 December 31 Total revenues $ 378,290 $ 397,613 $ 287,506 $ 204,901 Gross profit (1) $ 187,917 $ 184,406 $ 89,702 $ 55,713 Operating income $ 156,779 $ 147,945 $ 54,599 $ 24,071 Net income (3) $ 110,447 $ 125,481 $ 45,022 $ 20,751 Net income per share—basic (4) $ 2.14 $ 2.43 $ 0.88 $ 0.41 Net income per share—diluted (4) $ 2.14 $ 2.43 $ 0.87 $ 0.41 (1) Represents total revenues less cost of sales (exclusive of items shown separately below) and cost of other revenues (exclusive of items shown separately below) for each respective period. (2) Net income for the three months ended March 31, 2020 includes proceeds received for the Shared Services Claim and Hybrid Debt Claim of $1.8 million. Net loss for the three months ended December 31, 2020 includes settlement proceeds of $1.7 million related to other Walter Energy claims. (3) Net income for the three months ended March 31, 2019 includes a loss on early extinguishment of debt of $9.8 million. Net income includes proceeds received for the Shared Services Claim and Hybrid Debt Claim of $17.5 million and $5.3 million for the three months ended June 30, 2019 and September 30, 2019, respectively. Net income for the three months ended December 31, 2019 includes a change in ARO due to revisions to estimates of $7.8 million which is discussed further in Note 8. (4) The sum of quarterly amounts may not equal the annual amounts reported due to rounding. In addition, the sum of quarterly EPS amounts may be different than annual amounts as a result of the impact of variations in shares outstanding.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Concentrations of Credit Risk and Major Customers (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Concentration Risk [Line Items]
Other revenues	$ 212,253	$ 180,064	$ 163,701	$ 226,720	$ 204,901	$ 287,506	$ 397,613	$ 378,290	$ 782,738	$ 1,268,309	$ 1,378,007
Mining And Marketing Met Coal - Foreign Steel Customers | Sales Revenue, Net
Concentration Risk [Line Items]
Concentration risk, percentage									97.30%
Mining And Marketing Met Coal - Foreign Steel Customers | Trade Receivables
Concentration Risk [Line Items]
Concentration risk, percentage									96.80%
Customer Concentration Risk | Sales Revenue, Net | Xcoal Energy And Resources
Concentration Risk [Line Items]
Concentration risk, percentage									18.70%	22.30%	15.10%
Customer Concentration Risk | Sales Revenue, Net | Exiros BV Sucursal Uruguay
Concentration Risk [Line Items]
Concentration risk, percentage									15.00%	12.90%	11.00%
Customer Concentration Risk | Sales Revenue, Net | Iskenderun Demir Ve Celik
Concentration Risk [Line Items]
Concentration risk, percentage									11.40%
Customer Concentration Risk | Sales Revenue, Net | Arcelor
Concentration Risk [Line Items]
Concentration risk, percentage										10.40%
Customer Concentration Risk | Sales Revenue, Net | Thyssenkrupp Steel Europe AG
Concentration Risk [Line Items]
Concentration risk, percentage										10.10%
Customer Concentration Risk | Sales Revenue, Net | Huettenwerke Krupp Mannesmann GmBH
Concentration Risk [Line Items]
Concentration risk, percentage											10.50%
Europe | Geographic Concentration Risk | Sales Revenue, Net
Concentration Risk [Line Items]
Concentration risk, percentage									56.00%
South America | Geographic Concentration Risk | Sales Revenue, Net
Concentration Risk [Line Items]
Concentration risk, percentage									25.00%
Asia | Geographic Concentration Risk | Sales Revenue, Net
Concentration Risk [Line Items]
Concentration risk, percentage									19.00%
Sales
Concentration Risk [Line Items]
Other revenues									$ 761,871	$ 1,235,998	$ 1,342,683
Sales | Customer Concentration Risk | Sales Revenue, Net | Xcoal Energy And Resources
Concentration Risk [Line Items]
Other revenues									146,500	276,200	203,600
Sales | Customer Concentration Risk | Sales Revenue, Net | Exiros BV Sucursal Uruguay
Concentration Risk [Line Items]
Other revenues									117,700	159,600	148,500
Sales | Customer Concentration Risk | Sales Revenue, Net | Iskenderun Demir Ve Celik
Concentration Risk [Line Items]
Other revenues									$ 89,100
Sales | Customer Concentration Risk | Sales Revenue, Net | Arcelor
Concentration Risk [Line Items]
Other revenues										128,200
Sales | Customer Concentration Risk | Sales Revenue, Net | Thyssenkrupp Steel Europe AG
Concentration Risk [Line Items]
Other revenues										$ 125,500
Sales | Customer Concentration Risk | Sales Revenue, Net | Huettenwerke Krupp Mannesmann GmBH
Concentration Risk [Line Items]
Other revenues											$ 141,300

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Short-term Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule of Held-to-maturity Securities [Line Items]
Short-term investments	$ 8,504	$ 14,675
Cash And Fixed Income Securities
Schedule of Held-to-maturity Securities [Line Items]
Short-term investments	$ 8,500
Treasury bills
Schedule of Held-to-maturity Securities [Line Items]
Short-term investments		$ 14,700

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2020
Machinery and equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life	3 years
Machinery and equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life	10 years
Land Improvements and Buildings | Minimum
Property, Plant and Equipment [Line Items]
Useful life	15 years
Land Improvements and Buildings | Maximum
Property, Plant and Equipment [Line Items]
Useful life	30 years

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Owned and Leased Mineral Interests (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Depletion	$ 9.3	$ 9.9	$ 9.6
Minimum
Property, Plant and Equipment [Line Items]
Mineral rights, lease term	10 years
Maximum
Property, Plant and Equipment [Line Items]
Mineral rights, lease term	50 years

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Deferred Financing Costs (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Line of Credit Facility [Line Items]
Origination fees	$ (2,667)	$ (2,723)
ABL facility | Citibank
Line of Credit Facility [Line Items]
Origination fees	(3,500)	(4,200)
Senior Secured Notes Due 2024 | Senior secured notes
Line of Credit Facility [Line Items]
Unamortized deferred financing costs and debt discount	$ 2,700	$ 2,700

Inventories, net (Details)

Inventories, net (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Coal	$ 86,272	$ 69,064
Raw materials, parts, supplies and other, net	32,441	28,837
Total inventories, net	$ 118,713	$ 97,901

Prepaid Expenses and Other (Det

Prepaid Expenses and Other (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Deferred longwall move expenses	$ 22,972	$ 15,621
Prepaid insurance	3,832	3,631
Prepaid deposits	6,937	345
Other	6,169	4,247
Total prepaid expenses and other	$ 39,910	$ 23,844

Mineral Interests and Propert_3

Mineral Interests and Property, Plant and Equipment, Net - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Mineral interests	$ 144,200	$ 144,200
Mineral properties, accumulated depletion	(43,400)	(34,100)
Depreciation and depletion	$ 118,092	$ 97,330	$ 97,209

Mineral Interests and Propert_4

Mineral Interests and Property, Plant and Equipment, Net - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Financing lease right of use asset	$ 56,528	$ 44,996
Total	1,015,647	879,739
Less: Accumulated depreciation	(378,539)	(273,539)
Property, plant and equipment, net	637,108	606,200
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	71,886	72,267
Land improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	18,024	18,026
Building and leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	77,556	74,342
Mine development and infrastructure costs
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	29,893	13,315
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	679,393	614,687
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 82,367	$ 42,106

Other Long-Term Assets (Details

Other Long-Term Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Advance mining royalties	$ 7,305	$ 8,976
ABL Facility origination fees	2,667	2,723
Other	4,146	6,543
Total other long-term assets	$ 14,118	$ 18,242

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	Feb. 14, 2020	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Line Items]
Refunds received, amount		$ 24,300,000
Income taxes receivable			$ 0	$ 12,925,000
Long-term income taxes receivable			0	11,349,000
Income tax (benefit) expense			$ (20,144,000)	65,417,000	$ (225,814,000)
Effective tax rate			36.00%
IRC Section 451 marginal well credit			$ 3,977,000	0	4,964,000
Exercise price per Right (in dollars per share)	$ 31
(Loss) income before income tax (benefit) expense			(55,905,000)	367,116,000	470,973,000
Preferred Stock Purchase Right
Income Tax Disclosure [Line Items]
Rights to be issued per share of common stock (in shares)	1
Maximum threshold of beneficial ownership percentage acquired before dilution	4.99%
Maximum percentage of beneficial ownership held by existing stockholder before dilution of interest	5.00%
Redemption price per Right (in dollars per share)	$ 0.01
Federal
Income Tax Disclosure [Line Items]
Net operating loss carryforwards			920,700,000
Indefinite lived operating loss carryforwards			27,800,000
State
Income Tax Disclosure [Line Items]
Net operating loss carryforwards			995,800,000
Indefinite lived operating loss carryforwards			27,800,000
General business credits
Income Tax Disclosure [Line Items]
General business credit carryforward			$ 18,600,000
Release
Income Tax Disclosure [Line Items]
Income tax (benefit) expense				$ (225,800,000)	$ (225,814,000)

Income Taxes - Schedule of Inco

Income Taxes - Schedule of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current
Federal	$ (74)	$ (3,151)	$ (2,776)
State	5	85	0
Total current income tax expense (benefit)	(69)	(3,066)	(2,776)
Deferred
Federal	(16,731)	53,677	(176,141)
State	(3,344)	14,806	(46,897)
Total deferred income tax expense (benefit)	(20,075)	68,483	(223,038)
Tax (benefit) expense recognized	$ (20,144)	$ 65,417	$ (225,814)

Income Taxes - Income Tax Rate

Income Taxes - Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
(Loss) income before income tax (benefit) expense		$ (55,905)	$ 367,116	$ 470,973
Tax (benefit) expense at statutory tax rate		(11,740)	77,094	98,904
Effect of:
Depletion		(1,504)	(16,198)	(18,227)
Tax Cuts and Jobs Act impact		0	0	(2,775)
State and local income tax, net of federal effect		(2,637)	11,747	14,897
Valuation allowance on deferred tax assets		0	0	(312,493)
Non-deductible transaction costs		0	0	566
Impact of Walter Energy IRS Settlement (1)		0	(6,615)	0
IRC Section 451 marginal well credit		(3,977)	0	(4,964)
Other		(286)	(611)	(1,722)
Tax (benefit) expense recognized		(20,144)	65,417	(225,814)
Income tax receivable recorded during period	$ 6,600	$ (24,274)	$ (21,795)	$ 12,431

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred income tax assets:
Net operating loss and credit carryforwards	$ 253,756	$ 215,805
Inventory	0	457
Asset retirement obligations	15,547	14,115
Black lung obligations	9,275	8,168
Accrued expenses	4,303	5,597
Other	3,614	3,649
Total deferred income tax assets	286,495	247,791
Deferred income tax liabilities:
Inventory	(558)	0
Prepaid expenses	(10,470)	(8,514)
Property, plant and equipment	(98,637)	(82,539)
Other	(2,458)	(2,441)
Total deferred income tax liabilities	(112,123)	(93,494)
Net deferred income tax asset	$ 174,372	$ 154,297

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Asset Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred Tax Asset Valuation Roll Forward
Beginning balance		$ 0	$ 312,493
Income tax (benefit) expense	$ (20,144)	65,417	(225,814)
Ending balance			0
Addition/(Reduction) - current tax expense/(benefit)
Deferred Tax Asset Valuation Roll Forward
Additions (reduction)			(86,679)
Release
Deferred Tax Asset Valuation Roll Forward
Income tax (benefit) expense		$ (225,800)	$ (225,814)

Asset Retirement Obligations -

Asset Retirement Obligations - Schedule of Changes in Asset Retirement Obligations (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO, beginning balance		$ 56,206	$ 61,824
Accretion expense		3,004	3,169
Revisions to estimates	$ (7,800)	2,973	(7,825)
Obligations settled		(276)	(962)
ARO, ending balance	$ 56,206	$ 61,907	$ 56,206

Asset Retirement Obligations _2

Asset Retirement Obligations - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Loss Contingencies [Line Items]
Asset retirement obligations, current	$ 4,354,000	$ 2,623,000
Asset retirement obligations, noncurrent	57,553,000	53,583,000
Assets legally restricted to settle AROs	0
Adjustment to liability reflected in income	$ 400,000	$ 11,100,000
Adjustment to liability reflected in income (usd per share)	$ 0.01	$ 0.22
Surety Bond
Loss Contingencies [Line Items]
Loss contingency	$ 40,800,000
Letter of Credit
Loss Contingencies [Line Items]
Loss contingency	$ 3,600,000

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued wages and employee benefits	$ 25,539	$ 38,680
Accrued operating expenses	46,285	14,014
Accrued royalties	3,484	3,304
Accrued freight	2,724	1,971
Accrued interest	4,981	4,635
Accrued non-income taxes	3,095	3,151
Total accrued expenses	$ 86,108	$ 65,755

Pneumoconiosis ("Black Lung")_2

Pneumoconiosis ("Black Lung") Obligations (Details) - USD ($)	Feb. 21, 2020	Dec. 31, 2020	Dec. 31, 2019	May 31, 2020	Apr. 01, 2016
Self Insurance Reserve Disclosure [Abstract]
Deductible amount per black lung claim		$ 1,000,000		$ 500,000
Collateral securities					$ 17,000,000
Increase in collateral securities	$ 39,800,000
Surety Bonds		17,000,000	$ 17,000,000
Short-term investments		8,500,000	14,500,000
Black lung trust		3,000,000	3,300,000
Estimated total black lung liabilities		36,900,000	32,500,000
Black lung obligations, current		2,400,000	2,300,000
Black lung obligations, noncurrent		$ 34,567,000	$ 30,233,000

Employee Benefit Plans (Details

Employee Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
UMWA Collective Bargaining Agreement
Defined Contribution Plan Disclosure [Line Items]
Percent of company's employees represented	67.20%	68.20%
Successor Benefit Plan
Defined Contribution Plan Disclosure [Line Items]
Contributions to defined contribution plans	$ 3	$ 2.9	$ 3.1

Equity Award Plans - Narrative

Equity Award Plans - Narrative (Details) - USD ($) $ in Millions	Aug. 08, 2018	Jun. 14, 2018	May 10, 2018	Jun. 30, 2018	Dec. 31, 2020
2017 Equity Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense					$ 7.3
Unrecognized compensation expense					$ 3.5
Shares available for grant (in shares)					4,977,874
Restricted Stock | 2016 Equity Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)					805,083
Forfeited (in shares)					30,199
Vested (in shares)					722,663
Unvested (in shares)					52,221
Restricted Stock | 2016 Equity Plan | Tranche Six
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense					$ 0.3
Unrecognized compensation expense					$ 0.1
Restricted Stock | 2016 Equity Plan | Tranche Seven
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Forfeited (in shares)					25,551
Vested (in shares)					190,580
Award vesting percentage					50.00%
Shares issued in transaction (in shares)					268,352
Director | Phantom Share Units (PSUs) | 2016 Equity Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)					43,580
Expiration period					5 years
August Equity Offering
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued in transaction (in shares)	2,204,806	5,000,000	8,000,000	13,000,000
Incremental stock compensation expense				$ 3.6

Equity Award Plans - Schedule o

Equity Award Plans - Schedule of Restricted Stock (Details) - Restricted Stock Units (RSUs)	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Shares
Outstanding, end of period (in shares)	281,588
2017 Equity Plan
Shares
Nonvested, beginning of period (in shares)	503,892
Granted (in shares)	477,703
Canceled (in shares)	(633)
Forfeited (in shares)	(16,267)
Vested (in shares)	(165,455)
Outstanding, end of period (in shares)	799,240
Weighted Average Grant Date Fair Value
Nonvested, beginning of period (in dollars per share) | $ / shares	$ 21.57
Granted (in dollars per share) | $ / shares	12.38
Canceled (in dollars per share) | $ / shares	22.21
Forfeited (in dollars per share) | $ / shares	18.42
Vested (in dollars per share) | $ / shares	$ 26.04

Debt - Schedule of Long-Term De

Debt - Schedule of Long-Term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Debt discount, net	$ (3,527)	$ (4,246)
Long-term debt	379,908	339,189
Less: current debt	0	0
Total long-term debt	379,908	339,189
ABL facility
Debt Instrument [Line Items]
Long-term debt, gross	$ 40,000	0
Weighted Average Interest Rate	4.00%
Senior secured notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 343,435	$ 343,435
Weighted Average Interest Rate	8.00%

Debt - Minimum Debt Repayment S

Debt - Minimum Debt Repayment Schedule (Details) $ in Thousands	Dec. 31, 2020USD ($)
Debt Instrument [Line Items]
2020	$ 0
2021	0
2022	0
2023	40,000
2024	343,435
Thereafter	0
ABL facility
Debt Instrument [Line Items]
2020	0
2021	0
2022	0
2023	40,000
2024	0
Thereafter	0
Senior secured notes
Debt Instrument [Line Items]
2020	0
2021	0
2022	0
2023	0
2024	343,435
Thereafter	$ 0

Debt - Narrative (Details)

Debt - Narrative (Details)

Apr. 23, 2019USD ($)

Feb. 21, 2019USD ($)

Apr. 03, 2018USD ($)$ / shares

Mar. 01, 2018USD ($)

Nov. 02, 2017USD ($)$ / shares

Mar. 31, 2019USD ($)

Dec. 31, 2020USD ($)$ / shares

Dec. 31, 2019USD ($)$ / shares

Dec. 31, 2018USD ($)$ / shares

Jul. 20, 2020USD ($)

Mar. 25, 2019USD ($)

Mar. 22, 2019USD ($)

Oct. 15, 2018USD ($)

Debt Instrument [Line Items]

Cash dividends

$ 230,000,000

Dividends paid (in dollars per share) | $ / shares

$ 0.20

$ 4.61

$ 6.73

Debt issuance costs

$ 0

$ 0

$ 3,713,000

Amount that can be authorized without making an offer to buy back debt

$ 299,401,000

Loss on extinguishment of debt

$ 9,800,000

0

$ 9,756,000

0

Senior Secured Notes Due 2024 | Upon occurrence of a change in control

Debt Instrument [Line Items]

Redemption price, percentage

101.00%

Senior Secured Notes Due 2024 | Prior to making certain restricted payments

Debt Instrument [Line Items]

Redemption price, percentage

103.00%

Senior Secured Notes Due 2024 | Upon occurrence of asset sales or dispositions

Debt Instrument [Line Items]

Redemption price, percentage

100.00%

Senior secured notes | Senior Secured Notes Due 2024

Debt Instrument [Line Items]

Face amount of debt

$ 350,000,000

Stated interest rate

8.00%

Net proceeds from debt

$ 340,000,000

Payment of special cash dividend

260,000,000

Cash dividends

$ 600,000,000

Dividends paid (in dollars per share) | $ / shares

$ 11.21

Senior secured notes | Senior Secured Notes Due 2024, New Notes

Debt Instrument [Line Items]

Face amount of debt

$ 125,000,000

Payment of special cash dividend

$ 225,000,000

Cash dividends

$ 350,000,000

Dividends paid (in dollars per share) | $ / shares

$ 6.53

Redemption price, percentage

103.00%

Transaction costs

$ 6,400,000

Debt issuance costs

$ 3,700,000

Senior secured notes | Senior Secured Notes Due 2024, Existing Notes, Restricted Payment Offer

Debt Instrument [Line Items]

Redemption price, percentage

103.00%

Maximum amount available for repurchase

$ 150,000,000

Debt instrument, amount validly tendered and not withdrawn

$ 1,900,000

Pro-ration factor

31.5789%

Purchase integrals

$ 1,000

Senior secured notes | Senior Secured Notes Due 2024, Tendered Notes, Restricted Payment Pro-Rated Offer

Debt Instrument [Line Items]

Debt instrument, amount validly tendered and not withdrawn

599,000

Debt instrument, amount accepted

599,000

Debt instrument, not accepted

1,301,000

Senior secured notes | Senior Secured Notes Due 2024, Existing Notes, Tender Offer

Debt Instrument [Line Items]

Redemption price, percentage

104.25%

Maximum amount available for repurchase

$ 150,000,000

Debt instrument, amount validly tendered and not withdrawn

$ 415,099,000

Pro-ration factor

31.5789%

Purchase integrals

$ 1,000

Senior secured notes | Senior Secured Notes Due 2024, Tendered Notes, Tender Offer Pro-Rated Offer

Debt Instrument [Line Items]

Debt instrument, amount validly tendered and not withdrawn

130,966,000

Debt instrument, amount accepted

130,966,000

Debt instrument, not accepted

$ 284,133,000

ABL facility | Citibank

Debt Instrument [Line Items]

Aggregate lender commitment

$ 120,000,000

$ 125,000,000

Aggregate principal amount drawn

40,000,000

Remaining borrowing capacity

$ 31,600,000

Coverage ratio

1

ABL facility | Citibank | Swingline loan

Debt Instrument [Line Items]

Aggregate lender commitment

10,000,000

ABL facility | Citibank | Letter of credit

Debt Instrument [Line Items]

Aggregate lender commitment

$ 50,000,000

Letters of credit outstanding

$ 9,400,000

Leases - Narrative (Details)

Leases - Narrative (Details) $ in Millions	Dec. 31, 2020USD ($)
Lessor, Lease, Description [Line Items]
Finance lease that have not yet commenced	$ 1.6
Minimum
Lessor, Lease, Description [Line Items]
Remaining lease terms	1 year
Lease commencing terms	1 year
Maximum
Lessor, Lease, Description [Line Items]
Remaining lease terms	5 years
Lease commencing terms	2 years

Leases - Supplemental balance s

Leases - Supplemental balance sheet information (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Finance lease right-of-use assets, net	$ 46,746	$ 40,227
Finance lease liabilities
Current	14,385	10,146
Noncurrent	24,091	25,528
Total finance lease liabilities	$ 38,476	$ 35,674
Weighted average remaining lease term - finance leases (in months)	3 years 6 months 25 days	3 years 8 months 19 days
Weighted average discount rate - finance leases	5.77%	6.02%
Finance lease right-of-use assets, accumulated amortization	$ 9,800	$ 4,800

Leases - Components of lease ex

Leases - Components of lease expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease cost	$ 2,980	$ 2,527
Finance lease cost:
Amortization of leased assets	12,730	11,202
Interest on lease liabilities	1,988	1,761
Net lease cost	$ 17,698	$ 15,490

Leases - Maturities of lease li

Leases - Maturities of lease liabilities (Details) $ in Thousands	Dec. 31, 2020USD ($)
Leases [Abstract]
2021	$ 16,276
2022	12,555
2023	10,774
2024	2,557
2025	732
Thereafter	0
Total	42,894
Less: amount representing interest	(4,418)
Present value of lease liabilities	38,476
Future payments required under signed lease agreements that have not yet commenced	$ 1,600

Leases - Supplemental cash flow

Leases - Supplemental cash flow information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from finance leases	$ 1,988	$ 1,761
Financing cash flows from finance leases	14,237	17,273
Non-cash right-of-use assets obtained in exchange for lease obligations:
Finance leases	$ 18,967	$ 45,523	$ 6,822

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Nov. 05, 2015
Black Warrior Methane (BWM)
Related Party Transaction [Line Items]
Proportionate consolidation method, ownership percentage				50.00%
Black Warrior Transmission (BWT)
Related Party Transaction [Line Items]
Equity method investment, ownership percentage				50.00%
Allocated Expenses to Joint Venture | Corporate Joint Venture
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 2.6	$ 1.5	$ 3.2

Commitments and Contingencies (

Commitments and Contingencies (Details) - USD ($)	1 Months Ended	3 Months Ended				12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Guarantor Obligations [Line Items]
Proceeds received from claims	$ 1,800,000	$ 1,700,000	$ 1,800,000	$ 5,300,000	$ 17,500,000		$ 22,800,000
Coal royalty expense						$ 49,500,000	87,300,000	$ 101,000,000
Accrued expenses
Guarantor Obligations [Line Items]
Throughput obligation		$ 0				$ 0	$ 0

Stockholders' Equity (Details)

Stockholders' Equity (Details) - USD ($)	Aug. 08, 2018	Jun. 14, 2018	May 10, 2018	Jun. 30, 2018	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Mar. 31, 2019	Mar. 26, 2019	Mar. 25, 2019	May 02, 2018
Class of Stock [Line Items]
Shares repurchased, value						$ 12,546,000	$ 38,030,000
Remaining authorized repurchase amount										$ 299,401,000
The New Stock Repurchase Program
Class of Stock [Line Items]
Authorized amount									$ 70,000,000
Shares repurchased (in shares)					500,000
Shares repurchased, value					$ 10,600,000
Remaining authorized repurchase amount					$ 58,800,000	58,800,000
The Stock Repurchase Program
Class of Stock [Line Items]
Authorized amount											$ 40,000,000
Shares repurchased (in shares)			500,000
Remaining authorized repurchase amount								$ 1,900,000
Aggregate amount of repurchase			$ 12,100,000
August Equity Offering
Class of Stock [Line Items]
Shares issued in transaction (in shares)	2,204,806	5,000,000	8,000,000	13,000,000
Price per share (in dollars per share)	$ 25.40	$ 28.35	$ 24.20
Secondary Equity Offerings
Class of Stock [Line Items]
Payments of stock issuance costs						$ 2,700,000

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Details) $ in Millions	Dec. 31, 2020USD ($)
Senior secured notes | Senior Secured Notes Due 2024 | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of long-term debt	$ 352.5
ABL facility | ABL Facility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Remaining borrowing capacity	31.6
Citibank | ABL facility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Outstanding borrowings	40
Remaining borrowing capacity	31.6
Citibank | ABL facility | Letter of credit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Letters of credit outstanding	$ 9.4

Net (Loss) Income per Share - S

Net (Loss) Income per Share - Schedule of Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net (loss) income	$ (33,711)	$ (14,434)	$ (9,161)	$ 21,545	$ 20,751	$ 45,022	$ 125,481	$ 110,447	$ (35,761)	$ 301,699	$ 696,787
Denominator:
Weighted-average shares used to compute net income (loss) per share—basic (in shares)									51,168	51,363	52,812
Dilutive restricted stock awards and units (in shares)									0	130	106
Weighted-average shares used to compute net income (loss) per share—diluted (in shares)									51,168	51,493	52,918
Net (loss) income per share—basic (in dollars per share)	$ (0.66)	$ (0.28)	$ (0.18)	$ 0.42	$ 0.41	$ 0.88	$ 2.43	$ 2.14	$ (0.70)	$ 5.87	$ 13.19
Net (loss) income per share—diluted (in dollars per share)	$ (0.66)	$ (0.28)	$ (0.18)	$ 0.42	$ 0.41	$ 0.87	$ 2.43	$ 2.14	$ (0.70)	$ 5.86	$ 13.17

Net (Loss) Income per Share - N

Net (Loss) Income per Share - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Apr. 23, 2019	Apr. 03, 2018	May 17, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020
Class of Stock [Line Items]
Dilutive awards (in shares)				0	130,000	106,000
Dividends (in dollars per share)			$ 0.05
Cash dividends	$ 230,000
Quarterly dividends declared (in dollars per share)							$ 0.05
Dividends				$ 10,395	$ 240,394	$ 360,635	$ 39,500
Special cash dividend (in dollars per share)	$ 4.41
Restricted Stock Units (RSUs)
Class of Stock [Line Items]
Common stock issues to employees and directors, unvested (in shares)				281,588			281,588
Restricted Stock Units (RSUs) | 2017 Equity Plan
Class of Stock [Line Items]
Common stock issues to employees and directors, unvested (in shares)				799,240	503,892		799,240
Common stock shares issued (in shares)				13,157
Restricted Stock | 2016 Equity Plan
Class of Stock [Line Items]
Common stock issues to employees and directors, unvested (in shares)				52,221			52,221
Restricted Stock Units (RSUs), Service-Based Vesting Conditions | 2016 Equity Plan
Class of Stock [Line Items]
Antidilutive securities excluded from the computation of EPS (in shares)				52,221
Phantom Share Units (PSUs) | 2016 Equity Plan
Class of Stock [Line Items]
Common stock shares issued (in shares)				43,580
Phantom Share Units (PSUs) | 2016 and 2017 Equity Plans
Class of Stock [Line Items]
Settlement period				5 years
Restricted Stock | 2017 Equity Plan
Class of Stock [Line Items]
Antidilutive securities excluded from the computation of EPS (in shares)				447,295
Senior Secured Notes Due 2024, New Notes | Senior secured notes
Class of Stock [Line Items]
Cash dividends		$ 350,000
Payment of special cash dividend		$ 225,000

Segment Information (Details)

Segment Information (Details)	12 Months Ended
	Dec. 31, 2020segment
Segment Reporting [Abstract]
Number of operating segments	2
Number of reportable segments	1

Segment Information - Reconcili

Segment Information - Reconciliation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Other revenues	$ 212,253	$ 180,064	$ 163,701	$ 226,720	$ 204,901	$ 287,506	$ 397,613	$ 378,290	$ 782,738	$ 1,268,309	$ 1,378,007
Segment Reconciling Items
Segment Reporting Information [Line Items]
Other revenues									20,867	32,311	35,324
Mining | Operating Segments
Segment Reporting Information [Line Items]
Other revenues									$ 761,871	$ 1,235,998	$ 1,342,683

Segment Information - Reconci_2

Segment Information - Reconciliation of Capital Expenditures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Capital Expenditures	$ 87,488	$ 107,278	$ 101,620
Segment Reconciling Items
Segment Reporting Information [Line Items]
Capital Expenditures	9,473	6,510	4,013
Mining | Operating Segments
Segment Reporting Information [Line Items]
Capital Expenditures	$ 78,015	$ 100,768	$ 97,607

Segment Information - Reconci_3

Segment Information - Reconciliation of Net Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Segment Adjusted EBITDA									$ 136,701	$ 515,253	$ 626,038
Other revenues	$ 212,253	$ 180,064	$ 163,701	$ 226,720	$ 204,901	$ 287,506	$ 397,613	$ 378,290	782,738	1,268,309	1,378,007
Cost of other revenues									(33,736)	(29,828)	(10,172)
Depreciation and depletion									(118,092)	(97,330)	(97,209)
Selling, general and administrative									(32,879)	(37,014)	(36,626)
Transaction and other costs									0	0	(9,068)
Loss on early extinguishment of debt								(9,800)	0	(9,756)	0
Other income									3,544	22,815	0
Interest expense, net									(32,310)	(29,335)	(37,314)
Income tax (expense) benefit									20,144	(65,417)	225,814
Net (loss) income	$ (33,711)	$ (14,434)	$ (9,161)	$ 21,545	$ 20,751	$ 45,022	$ 125,481	$ 110,447	(35,761)	301,699	696,787
Other revenues
Segment Reporting Information [Line Items]
Other revenues									$ 20,867	$ 32,311	$ 35,324

Subsequent Events (Details)

Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Millions	Feb. 18, 2021	May 17, 2017
Subsequent Event [Line Items]
Dividends declared (in dollars per share)		$ 0.05
Subsequent Event
Subsequent Event [Line Items]
Dividends declared (in dollars per share)	$ 0.05
Dividends payable	$ 2.6

Supplemental Summary Quarterl_3

Supplemental Summary Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Total revenues		$ 212,253	$ 180,064	$ 163,701	$ 226,720	$ 204,901	$ 287,506	$ 397,613	$ 378,290	$ 782,738	$ 1,268,309	$ 1,378,007
Gross profit		9,275	21,630	25,282	67,645	55,713	89,702	184,406	187,917
Operating income (loss)		(37,778)	(14,527)	(5,331)	30,497	24,071	54,599	147,945	156,779	(27,139)	383,392	508,287
Net (loss) income		$ (33,711)	$ (14,434)	$ (9,161)	$ 21,545	$ 20,751	$ 45,022	$ 125,481	$ 110,447	$ (35,761)	$ 301,699	$ 696,787
Net (loss) income per share—basic (in dollars per share)		$ (0.66)	$ (0.28)	$ (0.18)	$ 0.42	$ 0.41	$ 0.88	$ 2.43	$ 2.14	$ (0.70)	$ 5.87	$ 13.19
Net (loss) income per share—diluted (in dollars per share)		$ (0.66)	$ (0.28)	$ (0.18)	$ 0.42	$ 0.41	$ 0.87	$ 2.43	$ 2.14	$ (0.70)	$ 5.86	$ 13.17
Proceeds received from claims	$ 1,800	$ 1,700			$ 1,800		$ 5,300	$ 17,500			$ 22,800
Loss on early extinguishment of debt									$ 9,800	$ 0	9,756	$ 0
Revision of ARO estimate						$ 7,800				$ (2,973)	$ 7,825