Significant Accounting Policies (Policies)	12 Months Ended
Dec. 31, 2021
Summary of Significant Accounting Policies.
Basis of Presentation	Basis of Presentation and Consolidation—The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and U.S. Securities and Exchange Commission regulations. The financial statements are presented on a consolidated basis for all periods presented. All significant intercompany balances and transactions between consolidated entities have been eliminated in consolidation.
Use of estimates	Use of estimates—The preparation of these financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect certain reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from those estimates. The most significant estimates are related to the quantity and value of coal inventories, stock-based compensation, asset retirement obligations, occupational disease obligations, evaluation of long-lived assets for impairment, and the quantities and values of coal reserves.
Revenue Recognition	Revenue Recognition—Our primary source of revenue is from the sale of coal through contracts with steel producers usually having durations of less than one year. Revenue is recognized when performance obligations under the terms of a contract with our customers are satisfied. This occurs when control of the coal is transferred to our customers. For coal shipments to domestic customers via rail, control is generally transferred when the railcar is loaded. Control is transferred for export coal shipments to customers via ocean vessel when the vessel is loaded at the port. Our coal sales generally include up to 90-day payment terms following the transfer of control of the goods to our customer. In the case of some of our foreign customers, our contracts also require that letters of credit are posted to secure payment of any outstanding receivable. We do not include extended payment terms in our contracts. Our contracts with customers typically provide for minimum specifications or qualities of the coal we deliver. Variances from these specifications or qualities are settled by means of price adjustments. Generally, these price adjustments are settled within 30 days of delivery and are insignificant. Freight Revenue and Expense—Costs incurred to transport coal to the point of sale at the port facility are included in cost of sales and the gross amounts billed to customers to cover shipping to and handling of the coal at the port are included in revenue.
Cash and cash equivalents	Cash and Cash Equivalents—We classify all highly-liquid instruments with an original maturity of three months or less as cash equivalents. Restricted cash balances at December 31, 2021 and 2020 were $0.9 million and $1.4 million, respectively, consisted of funds held in escrow for potential future workers’ compensation claims and were classified in other current assets in the consolidated balance sheets.
Inventories	Inventories— Coal is reported as inventory at the point in time it is extracted from the mine. Coal inventories are valued at the lower of average cost or net realizable value, with cost determined on a first-in, first-out inventory valuation method. Coal inventory costs include labor, supplies, equipment costs, freight, operating overhead, depreciation and amortization. Coal inventory quantities are adjusted periodically based on aerial surveys of coal stockpiles. Supply inventories are valued at average cost and totaled $2.6 million at December 31, 2021 and $2.5 million at December 31, 2020.
Property, Plant and Equipment	Property, Plant and Equipment—Property, plant and equipment is recorded at cost. Expenditures which extend the useful lives of existing plant and equipment are capitalized. Planned major maintenance costs which do not extend the useful lives of existing plant and equipment are expensed as incurred. When properties are retired or otherwise disposed, the related cost and accumulated depreciation are removed from the respective accounts and any profit or loss on disposition is recognized in the consolidated statements of operations. Coal exploration costs are expensed as incurred. Coal exploration costs include those incurred to ascertain existence, location, extent or quality of ore or minerals before beginning the development stage of the mine. Mining property and mineral rights costs represent the costs incurred to acquire the rights to access and mine certain coal property either through deeds, leases, or other conveyance agreements. These costs include costs of acquiring, and accessing mineral reserves, resources and surface areas for mining activities. Capitalized mine development costs represent the costs incurred to prepare mine sites and/or seams of coal for future mining. These costs include costs of acquiring, permitting, planning, research, and developing access to identified mineral reserves and other preparations for commercial production as necessary to develop and permit the properties for mining activities. Operating expenditures including certain professional fees and overhead costs are not capitalized but are expensed as incurred. The capitalized mine development costs are depleted or amortized on a units-of-production basis as mining of that mine’s assigned reserves takes place. Depreciation of plant and equipment is calculated on the straight-line method over their estimated useful lives ranging from three to thirty years.
Advanced Coal Royalties	Advanced Coal Royalties—In most cases, we acquire the right to mine coal reserves under leases which call for the payment of royalties on coal as it is mined and sold. In many cases, these mineral leases require the payment of advance or minimum coal royalties to lessors that are recoupable against future production royalties. These advance payments are deferred and charged to operations as the coal reserves are mined.
Impairment of Long-lived Assets	Impairment of Long-lived Assets—We review and evaluate long-lived assets, including property, plant and equipment and mine development costs, for impairment when events or changes in circumstances indicate that the asset’s carrying value may not be recoverable. Recoverability is measured by comparing the net book value to the fair value. When the net book value exceeds the fair value, an impairment loss is measured and recorded. If it is determined that an undeveloped mineral interest cannot be economically converted to proven and probable reserves, or that the recoverability of capitalized mine development costs is uncertain, such capitalized costs are reduced to their net realizable value and an impairment loss is recorded to expense and future development costs are expensed as incurred.
Asset Retirement Obligations	Asset Retirement Obligations—Legal obligations associated with the retirement of long-lived assets are reflected at their estimated fair value, with a corresponding charge to development costs, at the time they are incurred. Our asset retirement obligations primarily consist of spending estimates related to reclaiming metallurgical coal land and support facilities in accordance with federal and state reclamation laws as defined by each mining permit. We estimate and record the fair value of a liability for an asset retirement obligation in the period in which it is incurred and a corresponding increase in the carrying amount of the related long-lived asset. The liability is accreted to its present value each period and the capitalized cost is amortized using the units-of-production method over estimated recoverable reserves upon commencement of mining. Occupational Disease (Pneumoconiosis) Obligations. We recognize as a liability to provide for occupational disease (pneumoconiosis) benefits to eligible employees, former employees and dependents as required by the Federal Mine Safety and Health Act of 1969, as amended. The occupational disease benefit obligation represents the present value of the actuarially computed present and future liabilities for such benefits over the employees’ applicable years of service using a discount rate. Estimating the future occupational disease (pneumoconiosis) benefits requires management to make estimates and judgments regarding timing and existence of a liability utilizing third-party actuaries to assist in preparing what constitutes adequate liability amounts. Inherent in the fair value calculation are numerous assumptions and judgments including the ultimate costs, inflation factors, credit adjusted discount rates, timing of settlement awards in the legal and regulatory environments. These estimates are subject to uncertainty due to a variety of factors, including extended lag times in the reporting and resolution of claims, and trends or changes in claim settlement patterns, insurance industry practices and legal interpretations. As a result, actual costs could differ significantly from the estimated amounts. Adjustments to estimated liabilities are recorded in the period in which the change in estimate occurs.
Deferred income	Deferred Income—We accounted for the SBA Paycheck Protection Program Loan (“PPP Loan”) as an in-substance government grant because we expected to meet the PPP Loan eligibility criteria and concluded that the loan represents, in substance, a grant that is expected to be forgiven. Proceeds from the PPP Loan were initially recognized as a deferred income liability. Subsequently, we reduced this liability and recognized income on a systematic basis over the period in which the related costs for which the PPP Loan was intended were incurred. PPP Loan income is presented as other income within the consolidated statements of operations.
Leases	Leases—We determine if an arrangement is an operating lease or financing lease at inception. Leases are capitalized on the balance sheet as right-of-use (“ROU”) assets and obligations. ROU assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. Operating and financing lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. As most of our leases do not provide an implicit rate, we generally use our incremental borrowing rate based on the estimated rate of interest for collateralized borrowing over a similar term of the lease payments at commencement date. The operating and financing lease ROU assets also includes any lease payments made and excludes lease incentives. Our lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise that option. Lease expense for operating lease payments is recognized on a straight-line basis over the lease term. Financing lease obligations for financing lease payments are reduced over the lease term according to an amortization schedule. Leases of mineral reserves are exempted under U.S. GAAP from recognition as on the consolidated balance sheets.
Fair Value Measurements	Fair Value Measurements— For assets and liabilities that are recognized or disclosed at fair value in the consolidated financial statements, 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. We use a three-level fair value hierarchy that categorizes assets and liabilities measured at fair value based on the observability of the inputs utilized in the valuation. These levels include: Level 1 - inputs are quoted prices in active markets for the identical assets or liabilities; Level 2 - inputs are other than quoted prices included in Level 1 that are directly or indirectly observable through market-corroborated inputs; and Level 3 - inputs are unobservable, or observable but cannot be market-corroborated, requiring us to make assumptions about pricing by market participants.
Income Taxes	Income Taxes—Income tax expense (benefit) includes Federal and state income taxes. Certain income and expenses are not reported in tax returns and financial statements in the same year. The tax effect of such temporary differences is reported as deferred income taxes. We account for deferred income taxes by applying statutory tax rates in effect at the reporting date of the balance sheet. A valuation allowance is established if it is more likely than not that the related tax benefits will not be realized. In determining the appropriate valuation allowance, we consider the projected realization of tax benefits based on expected levels of future taxable income, available tax planning strategies and reversals of existing taxable temporary differences. Uncertain tax positions are recognized 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. We had no unrecognized tax positions at December 31, 2021 and 2020. We file income tax returns in the U.S. and in various state and local jurisdictions which may be routinely examined by tax authorities. The statute of limitations is currently open for all tax returns filed.
Segment Reporting	Segment Reporting—Our properties located in West Virginia, Virginia and Pennsylvania each consist of mineral reserves for production of metallurgical coal from both underground and surface mines. These operations are within the Appalachia basin. Geology, coal transportation routes to customers, regulatory environments and coal quality or type are characteristic to a basin. For financial reporting purposes, these operations represent a single segment because each possesses similar production methods, distribution methods, and customer quality and consumption characteristics, resulting in similar long-term expected financial performance.
Stock-Based Compensation	Stock-Based Compensation—We account for employee stock-based compensation using the fair value method. Compensation cost for equity incentive awards is based on the fair value of the equity instrument generally on the date of grant and is recognized over the requisite service period. Forfeitures are recognized as they occur. The fair value of restricted stock awards is determined using the publicly-traded price of our common stock on the grant date. The fair value of option awards is calculated using the Black-Scholes option-pricing model. The Black-Scholes model requires us to make assumptions and judgments about the variables used in the calculation, including the expected term, expected volatility, risk-free interest rate, dividend rate and service period.
Concentrations	Concentrations—Our operations are all related to metallurgical coal within the mining industry. A reduction in metallurgical coal prices or other disturbances in the metallurgical coal markets could have an adverse effect on our operations. In 2021, 2020 and 2019, approximately 51%, 71% and 74%, respectively, of our revenue was derived from coal shipments to customers in North American markets. Financial instruments that potentially subject us to a significant concentration of credit risk consist primarily of cash and cash equivalents, restricted cash and accounts receivable. We maintain deposits in federally insured financial institutions in excess of federally insured limits. We monitor the credit ratings and concentration of risk with these financial institutions on a continuing basis to safeguard cash deposits. We have a limited number of customers. Contracts with these customers provide for billings principally upon shipment and compliance with payment terms is monitored on an ongoing basis. Outstanding receivables beyond payment terms are promptly investigated and discussed with the specific customer. We estimate an allowance for doubtful accounts based on an analysis of specific customers, taking into consideration the age of past due accounts and an assessment of the customer’s ability to pay. An allowance for doubtful accounts was not necessary as of December 31, 2021 and 2020. During 2021, sales to three customers accounted for approximately 58% of total revenue. The total balance due from these customers at December 31, 2021 was approximately 58% of total accounts receivable. During 2020, sales to three customers accounted for approximately 70% of total revenue. The total balance due from these customers at December 31, 2020 was approximately 46% of total accounts receivable. During 2019, sales to three customers accounted for approximately 53% of total revenue.
Reclassifications	Reclassifications—Financial statements presented for prior periods include reclassifications that were made to conform to the current-year presentation.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Adopted—In February 2016, the FASB issued ASU 2016-02, Leases, which aims to make leasing activities more transparent and comparable and requires substantially all leases be recognized by lessees on their balance sheet as a right-of-use asset and corresponding lease liability, including leases currently accounted for as operating leases. Leases of mineral reserves and related land leases are exempted from the standard. We adopted ASU 2016-02 on January 1, 2019. We elected the “package of practical expedients” within the standard which permits us not to reassess prior conclusions about lease identification, lease classification and initial direct costs. We made an accounting policy election to not separate lease and non-lease components for all leases. The adoption of this standard resulted in the recognition of right-of-use assets and lease liabilities of $0.3 million in 2020, which were not previously recorded on our consolidated balance sheet. In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses, which replaces the existing incurred loss impairment model with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. We adopted this standard effective January 1, 2020. The adoption of this ASU did not have a material impact on our consolidated financial statements because we do not have a history of credit losses on our financial instruments and have no material expected losses. In August 2018, the FASB issued ASU 2018-15, Internal-Use Software, which addresses the accounting for implementation costs associated with a hosted service. The standard provides that implementation costs be evaluated for capitalization using the same criteria as that used for internal-use software development costs, with amortization expense being recorded in the same income statement expense line as the hosted service costs and over the expected term of the hosting arrangement. We adopted this standard as of January 1, 2020 on a prospective basis. The adoption of this ASU did not have a material impact on our consolidated financial statements. In December 2019, the FASB issued ASU 2019-12, Income Taxes, which enhances and simplifies various aspects of the income tax accounting guidance, including requirements such as tax basis step-up in goodwill obtained in a transaction that is not a business combination, ownership changes in investments, and interim-period accounting for enacted changes in tax law. The standard was effective for us in the first quarter of 2021. The adoption of this ASU did not have a material impact on our consolidated financial statements. Recent Accounting Pronouncements Being Assessed—In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which provides optional expedients and exceptions for applying generally accepted accounting principles to contracts, hedging relationships, and other transactions affected by reference rate reform if certain criteria are met. The amendments are effective for all entities beginning on March 12, 2020 through December 31, 2022. The Company may elect to apply the amendments prospectively through December 31, 2022. The Company has not adopted this ASU as of December 31, 2021. The Company is currently assessing the impact of adopting this standard on its financial statements and the timing of adoption.

Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2021

Summary of Significant Accounting Policies.

Basis of Presentation and Consolidation—The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and U.S. Securities and Exchange Commission regulations. The financial statements are presented on a consolidated basis for all periods presented. All significant intercompany balances and transactions between consolidated entities have been eliminated in consolidation.

Use of estimates

Use of estimates—The preparation of these financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect certain reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from those estimates. The most significant estimates are related to the quantity and value of coal inventories, stock-based compensation, asset retirement

obligations, occupational disease obligations, evaluation of long-lived assets for impairment, and the quantities and values of coal reserves.

Revenue Recognition

Revenue Recognition—Our primary source of revenue is from the sale of coal through contracts with steel producers usually having durations of less than one year. Revenue is recognized when performance obligations under the terms of a contract with our customers are satisfied. This occurs when control of the coal is transferred to our customers. For coal shipments to domestic customers via rail, control is generally transferred when the railcar is loaded. Control is transferred for export coal shipments to customers via ocean vessel when the vessel is loaded at the port.

Our coal sales generally include up to 90-day payment terms following the transfer of control of the goods to our customer. In the case of some of our foreign customers, our contracts also require that letters of credit are posted to secure payment of any outstanding receivable. We do not include extended payment terms in our contracts. Our contracts with customers typically provide for minimum specifications or qualities of the coal we deliver. Variances from these specifications or qualities are settled by means of price adjustments. Generally, these price adjustments are settled within 30 days of delivery and are insignificant.

Freight Revenue and Expense—Costs incurred to transport coal to the point of sale at the port facility are included in cost of sales and the gross amounts billed to customers to cover shipping to and handling of the coal at the port are included in revenue.

Cash and cash equivalents

Cash and Cash Equivalents—We classify all highly-liquid instruments with an original maturity of three months or less as cash equivalents. Restricted cash balances at December 31, 2021 and 2020 were $0.9 million and $1.4 million, respectively, consisted of funds held in escrow for potential future workers’ compensation claims and were classified in other current assets in the consolidated balance sheets.

Inventories

Inventories— Coal is reported as inventory at the point in time it is extracted from the mine. Coal inventories are valued at the lower of average cost or net realizable value, with cost determined on a first-in, first-out inventory valuation method. Coal inventory costs include labor, supplies, equipment costs, freight, operating overhead, depreciation and amortization. Coal inventory quantities are adjusted periodically based on aerial surveys of coal stockpiles. Supply inventories are valued at average cost and totaled $2.6 million at December 31, 2021 and $2.5 million at December 31, 2020.

Property, Plant and Equipment

Property, Plant and Equipment—Property, plant and equipment is recorded at cost. Expenditures which extend the useful lives of existing plant and equipment are capitalized. Planned major maintenance costs which do not extend the useful lives of existing plant and equipment are expensed as incurred. When properties are retired or otherwise disposed, the related cost and accumulated depreciation are removed from the respective accounts and any profit or loss on disposition is recognized in the consolidated statements of operations.

Coal exploration costs are expensed as incurred. Coal exploration costs include those incurred to ascertain existence, location, extent or quality of ore or minerals before beginning the development stage of the mine.

Mining property and mineral rights costs represent the costs incurred to acquire the rights to access and mine certain coal property either through deeds, leases, or other conveyance agreements. These costs include costs of acquiring, and accessing mineral reserves, resources and surface areas for mining activities.

Capitalized mine development costs represent the costs incurred to prepare mine sites and/or seams of coal for future mining. These costs include costs of acquiring, permitting, planning, research, and developing access to identified mineral reserves and other preparations for commercial production as necessary to develop and permit the properties for mining activities. Operating expenditures including certain professional fees and overhead costs are not capitalized but are expensed as incurred.

The capitalized mine development costs are depleted or amortized on a units-of-production basis as mining of that mine’s assigned reserves takes place. Depreciation of plant and equipment is calculated on the straight-line method over their estimated useful lives ranging from three to thirty years.

Advanced Coal Royalties

Advanced Coal Royalties—In most cases, we acquire the right to mine coal reserves under leases which call for the payment of royalties on coal as it is mined and sold. In many cases, these mineral leases require the payment of advance or minimum coal royalties to lessors that are recoupable against future production royalties. These advance payments are deferred and charged to operations as the coal reserves are mined.

Impairment of Long-lived Assets

Impairment of Long-lived Assets—We review and evaluate long-lived assets, including property, plant and equipment and mine development costs, for impairment when events or changes in circumstances indicate that the asset’s carrying value may not be recoverable. Recoverability is measured by comparing the net book value to the fair value. When the net book value exceeds the fair value, an impairment loss is measured and recorded.

If it is determined that an undeveloped mineral interest cannot be economically converted to proven and probable reserves, or that the recoverability of capitalized mine development costs is uncertain, such capitalized costs are reduced to their net realizable value and an impairment loss is recorded to expense and future development costs are expensed as incurred.

Asset Retirement Obligations

Asset Retirement Obligations—Legal obligations associated with the retirement of long-lived assets are reflected at their estimated fair value, with a corresponding charge to development costs, at the time they are incurred. Our asset retirement obligations primarily consist of spending estimates related to reclaiming metallurgical coal land and support facilities in accordance with federal and state reclamation laws as defined by each mining permit. We estimate and record the fair value of a liability for an asset retirement obligation in the period in which it is incurred and a corresponding increase in the carrying amount of the related long-lived asset. The liability is accreted to its present value each period and the capitalized cost is amortized using the units-of-production method over estimated recoverable reserves upon commencement of mining.

Occupational Disease (Pneumoconiosis) Obligations. We recognize as a liability to provide for occupational disease (pneumoconiosis) benefits to eligible employees, former employees and dependents as required by the Federal Mine Safety and Health Act of 1969, as amended. The occupational disease benefit obligation represents the present value of the actuarially computed present and future liabilities for such benefits over the employees’ applicable years of service using a discount rate.

Estimating the future occupational disease (pneumoconiosis) benefits requires management to make estimates and judgments regarding timing and existence of a liability utilizing third-party actuaries to assist in preparing what constitutes adequate liability amounts. Inherent in the fair value calculation are numerous assumptions and judgments including the ultimate costs, inflation factors, credit adjusted discount rates, timing of settlement awards in the legal and regulatory environments. These estimates are subject to uncertainty due to a variety of factors, including extended lag times in the reporting and resolution of claims, and trends or changes in claim settlement patterns, insurance industry practices and legal interpretations. As a result, actual costs could differ significantly from the estimated amounts. Adjustments to estimated liabilities are recorded in the period in which the change in estimate occurs.

Deferred income

Deferred Income—We accounted for the SBA Paycheck Protection Program Loan (“PPP Loan”) as an in-substance government grant because we expected to meet the PPP Loan eligibility criteria and concluded that the loan represents, in substance, a grant that is expected to be forgiven. Proceeds from the PPP Loan were initially recognized as a deferred income liability. Subsequently, we reduced this liability and recognized income on a systematic basis over the period in which the related costs for which the PPP Loan was intended were incurred. PPP Loan income is presented as other income within the consolidated statements of operations.

Leases

Leases—We determine if an arrangement is an operating lease or financing lease at inception. Leases are capitalized on the balance sheet as right-of-use (“ROU”) assets and obligations.

ROU assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. Operating and financing lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. As most of our leases do not provide an implicit rate, we generally use our incremental borrowing rate based on the estimated rate of interest for collateralized borrowing over a similar term of the lease payments at commencement date. The operating and

financing lease ROU assets also includes any lease payments made and excludes lease incentives. Our lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise that option. Lease expense for operating lease payments is recognized on a straight-line basis over the lease term. Financing lease obligations for financing lease payments are reduced over the lease term according to an amortization schedule.

Leases of mineral reserves are exempted under U.S. GAAP from recognition as on the consolidated balance sheets.

Fair Value Measurements

Fair Value Measurements— For assets and liabilities that are recognized or disclosed at fair value in the consolidated financial statements, 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. We use a three-level fair value hierarchy that categorizes assets and liabilities measured at fair value based on the observability of the inputs utilized in the valuation. These levels include: Level 1 - inputs are quoted prices in active markets for the identical assets or liabilities; Level 2 - inputs are other than quoted prices included in Level 1 that are directly or indirectly observable through market-corroborated inputs; and Level 3 - inputs are unobservable, or observable but cannot be market-corroborated, requiring us to make assumptions about pricing by market participants.

Income Taxes

Income Taxes—Income tax expense (benefit) includes Federal and state income taxes. Certain income and expenses are not reported in tax returns and financial statements in the same year. The tax effect of such temporary differences is reported as deferred income taxes. We account for deferred income taxes by applying statutory tax rates in effect at the reporting date of the balance sheet. A valuation allowance is established if it is more likely than not that the related tax benefits will not be realized. In determining the appropriate valuation allowance, we consider the projected realization of tax benefits based on expected levels of future taxable income, available tax planning strategies and reversals of existing taxable temporary differences.

Uncertain tax positions are recognized 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. We had no unrecognized tax positions at December 31, 2021 and 2020. We file income tax returns in the U.S. and in various state and local jurisdictions which may be routinely examined by tax authorities. The statute of limitations is currently open for all tax returns filed.

Segment Reporting

Segment Reporting—Our properties located in West Virginia, Virginia and Pennsylvania each consist of mineral reserves for production of metallurgical coal from both underground and surface mines. These operations are within the Appalachia basin. Geology, coal transportation routes to customers, regulatory environments and coal quality or type are characteristic to a basin. For financial reporting purposes, these operations represent a single segment because each possesses similar production methods, distribution methods, and customer quality and consumption characteristics, resulting in similar long-term expected financial performance.

Stock-Based Compensation

Stock-Based Compensation—We account for employee stock-based compensation using the fair value method. Compensation cost for equity incentive awards is based on the fair value of the equity instrument generally on the date of grant and is recognized over the requisite service period. Forfeitures are recognized as they occur.

The fair value of restricted stock awards is determined using the publicly-traded price of our common stock on the grant date. The fair value of option awards is calculated using the Black-Scholes option-pricing model. The Black-Scholes model requires us to make assumptions and judgments about the variables used in the calculation, including the expected term, expected volatility, risk-free interest rate, dividend rate and service period.

Concentrations

Concentrations—Our operations are all related to metallurgical coal within the mining industry. A reduction in metallurgical coal prices or other disturbances in the metallurgical coal markets could have an adverse effect on our operations. In 2021, 2020 and 2019, approximately 51%, 71% and 74%, respectively, of our revenue was derived from coal shipments to customers in North American markets.

Financial instruments that potentially subject us to a significant concentration of credit risk consist primarily of cash and cash equivalents, restricted cash and accounts receivable. We maintain deposits in federally insured financial

institutions in excess of federally insured limits. We monitor the credit ratings and concentration of risk with these financial institutions on a continuing basis to safeguard cash deposits.

We have a limited number of customers. Contracts with these customers provide for billings principally upon shipment and compliance with payment terms is monitored on an ongoing basis. Outstanding receivables beyond payment terms are promptly investigated and discussed with the specific customer. We estimate an allowance for doubtful accounts based on an analysis of specific customers, taking into consideration the age of past due accounts and an assessment of the customer’s ability to pay. An allowance for doubtful accounts was not necessary as of December 31, 2021 and 2020.

During 2021, sales to three customers accounted for approximately 58% of total revenue. The total balance due from these customers at December 31, 2021 was approximately 58% of total accounts receivable. During 2020, sales to three customers accounted for approximately 70% of total revenue. The total balance due from these customers at December 31, 2020 was approximately 46% of total accounts receivable. During 2019, sales to three customers accounted for approximately 53% of total revenue.

Reclassifications

Reclassifications—Financial statements presented for prior periods include reclassifications that were made to conform to the current-year presentation.

Recent Accounting Pronouncements

Recent Accounting Pronouncements Adopted—In February 2016, the FASB issued ASU 2016-02, Leases, which aims to make leasing activities more transparent and comparable and requires substantially all leases be recognized by lessees on their balance sheet as a right-of-use asset and corresponding lease liability, including leases currently accounted for as operating leases. Leases of mineral reserves and related land leases are exempted from the standard. We adopted ASU 2016-02 on January 1, 2019. We elected the “package of practical expedients” within the standard which permits us not to reassess prior conclusions about lease identification, lease classification and initial direct costs. We made an accounting policy election to not separate lease and non-lease components for all leases. The adoption of this standard resulted in the recognition of right-of-use assets and lease liabilities of $0.3 million in 2020, which were not previously recorded on our consolidated balance sheet.

In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses, which replaces the existing incurred loss impairment model with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. We adopted this standard effective January 1, 2020. The adoption of this ASU did not have a material impact on our consolidated financial statements because we do not have a history of credit losses on our financial instruments and have no material expected losses.

In August 2018, the FASB issued ASU 2018-15, Internal-Use Software, which addresses the accounting for implementation costs associated with a hosted service. The standard provides that implementation costs be evaluated for capitalization using the same criteria as that used for internal-use software development costs, with amortization expense being recorded in the same income statement expense line as the hosted service costs and over the expected term of the hosting arrangement. We adopted this standard as of January 1, 2020 on a prospective basis. The adoption of this ASU did not have a material impact on our consolidated financial statements.

In December 2019, the FASB issued ASU 2019-12, Income Taxes, which enhances and simplifies various aspects of the income tax accounting guidance, including requirements such as tax basis step-up in goodwill obtained in a transaction that is not a business combination, ownership changes in investments, and interim-period accounting for enacted changes in tax law. The standard was effective for us in the first quarter of 2021. The adoption of this ASU did not have a material impact on our consolidated financial statements.

Recent Accounting Pronouncements Being Assessed—In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which provides optional expedients and exceptions for applying generally accepted accounting principles to contracts, hedging relationships, and other transactions affected by reference rate reform if certain criteria are met. The amendments are effective for all entities beginning on March 12, 2020 through December 31, 2022. The Company may elect to apply the

amendments prospectively through December 31, 2022. The Company has not adopted this ASU as of December 31, 2021. The Company is currently assessing the impact of adopting this standard on its financial statements and the timing of adoption.