Significant Accounting Policies (Policies)	12 Months Ended
Significant Accounting Policies (Policies)	Dec. 31, 2019
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates: The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and judgments. These estimates and judgments affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities (if any) at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents: Cash and cash equivalents include cash in banks and highly liquid investments with original maturities of three months or less.
Inventories	Inventories: Inventories are stated at the lower of cost or net realizable value. The weighted average method is used for inventory valuation.
Property, Plant and Equipment, Net	Property, Plant and Equipment, Net: Property, plant and equipment are initially recorded at cost. Depreciation, depletion and amortization are provided in amounts sufficient to amortize the cost of the assets, including assets recorded under finance leases, over their estimated useful lives using the straight-line method or the units-of-production method. Buildings and building improvements are depreciated over the life of the mine, which is generally 30 years. Estimated lives for machinery and equipment range from three to 15 years. The units-of-production method is used to amortize certain assets based on estimated recoverable tonnages. Repairs and maintenance costs are expensed when incurred, unless such costs extend the estimated useful life of the asset, in which case such costs are capitalized and depreciated. Asset retirement costs associated with asset retirement obligations are capitalized with the carrying amount of the related long-lived asset and depreciated over the asset's estimated useful life.
Long-Lived Assets	Long-Lived Assets: The Company periodically evaluates long-lived assets for impairment when changes in circumstances or the occurrence of certain events indicate the carrying amount of an asset or asset group may not be recoverable. Upon identification of indicators of impairment, the Company evaluates the carrying value of the asset by comparing the estimated future undiscounted cash flows generated from the use of the asset and its eventual disposition with the asset's net carrying value. If the carrying value of an asset is considered impaired, an impairment charge is recorded for the amount that the carrying value of the long-lived asset exceeds its fair value. Fair value is estimated 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.
Coal Supply Agreement	Coal Supply Agreement: The coal supply agreement represents a long-term supply agreement with MLMC's customer and was recorded based on the fair value at the date of acquisition. The coal supply agreement is amortized based on units of production over the term of the agreement, which is estimated to be 30 years. The Company reviews identified intangible assets for impairment when changes in circumstances or the occurrence of certain events indicate potential impairment.
Self-insurance Liabilities	Self-insurance Liabilities: The Company is generally self-insured for medical claims, certain workers’ compensation claims and certain closed mine liabilities. An estimated provision for claims reported and for claims incurred but not yet reported under the self-insurance programs is recorded and revised periodically based on industry trends, historical experience and management judgment. In addition, industry trends are considered within management's judgment for valuing claims. Changes in assumptions for such matters as legal judgments and settlements, inflation rates, medical costs and actual experience could cause estimates to change in the near term.
Revenue Recognition	Revenue Recognition:
Stock Compensation	Stock Compensation: The Company maintains long-term incentive programs that allow for the grant of shares of Class A common stock, subject to restrictions, as a means of retaining and rewarding selected employees for long-term performance and to increase ownership in the Company. Shares awarded under the plans are fully vested and entitle the stockholder to all rights of common stock ownership except that shares may not be assigned, pledged or otherwise transferred during the restriction period. In general, for shares awarded for years ended December 31, 2019 and December 31, 2018, the restriction period ends at the earliest of (i)three years after the participant's retirement date, (ii) three, five or ten years from the award date, or (iii) the participant's death or permanent disability. Pursuant to the plans, the Company issued 85,567 and 96,153 shares related to the years ended December 31, 2019 and 2018, respectively. After the issuance of these shares, there were 414,433 shares of Class A common stock available for issuance under these plans. Compensation expense related to these share awards was $4.1 million ($3.3 million net of tax) and $3.4 million ($2.7 million net of tax) for the years ended December 31, 2019 and 2018, respectively. Compensation expense represents fair value based on the market price of the shares of Class A common stock at the grant date. The Company also has a stock compensation plan for non-employee directors of the Company under which a portion of the annual retainer for each non-employee director is paid in restricted shares of Class A common stock. For the year ended December 31, 2019, $95,000 ($150,000 for the Chairman) of the non-employee director's annual retainer of $155,000 ($250,000 for the Chairman) was paid in restricted shares of Class A common stock. For the year ended December 31, 2018, $90,000 of the non-employee director's annual retainer of $150,000 was paid in restricted shares of Class A common stock. Shares awarded under the plan are fully vested and entitle the stockholder to all rights of common stock ownership except that shares may not be assigned, pledged or otherwise transferred during the restriction period. In general, the restriction period ends at the earliest of (i) ten years from the award date, (ii) the date of the director's death or permanent disability, (iii) five years (or earlier with the approval of the Board of Directors) after the director's date of retirement from the Board of Directors, or (iv) the date the director has both retired from the Board of Directors and has reached age 70. Pursuant to this plan, the Company issued 22,258 and 26,968 shares related to the years ended December 31, 2019 and 2018, respectively. In addition to the mandatory retainer fee received in restricted stock, directors may elect to receive shares of Class A common stock in lieu of cash for up to 100% of the balance of their annual retainer, committee retainer and any committee chairman's fees. These voluntary shares are not subject to any restrictions. Total shares issued under voluntary elections were 432 in 2019 and 560 in 2018. After the issuance of these shares, there were 77,310 shares of Class A common stock available for issuance under this plan. Compensation expense related to these awards was $1.1 million ($0.9 million net of tax) and $0.9 million ($0.7 million net of tax) for the years ended December 31, 2019 and 2018, respectively. Compensation expense represents fair value based on the market price of the shares of Class A common stock at the grant date.
Financial Instruments	Financial Instruments: Financial instruments held by the Company include cash and cash equivalents, accounts receivable, accounts payable, revolving credit agreements and long-term debt.
Fair Value Measurements	Fair Value Measurements: The Company accounts for the fair value measurement of its financial assets and liabilities in accordance with U.S. generally accepted accounting principles, which defines fair value 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 fair value hierarchy requires an entity to maximize the use of observable inputs, where available, and minimize the use of unobservable inputs when measuring fair value. Described below are the three levels of inputs that may be used to measure fair value: Level 1 - Quoted prices in active markets that are accessible at the measurement date for identical assets or liabilities. Level 2 - Observable prices that are based on inputs not quoted on active markets, but corroborated by market data. Level 3 - Unobservable inputs are used when little or no market data is available. The hierarchy is based upon the transparency of inputs to the valuation of an asset or liability as of the measurement date. The classification of fair value measurements within the hierarchy is based upon the lowest level of input that is significant to the measurement.
Recently Issued Accounting Standards	Recently Issued Accounting Standards Accounting Standards Adopted in 2019: NACCO adopted Accounting Standard Update ("ASU") 2016-02, Leases (Topic 842), which is codified in Accounting Standards Codification 842, Leases (“ASC 842”), on January 1, 2019, using the modified retrospective transition method (the "guidance").