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Priced coal supply commitment

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Proceeds From Sale Of Equity Method Investments Net Of Commissions Paid

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Year Supply Commitments End

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Value of input used to measure debt instrument, including, but not limited to, convertible and non-convertible debt.

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The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

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Date the declared dividend will be paid, in CCYY-MM-DD format.

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The per share amount of a dividend declared, but not paid, as of the financial reporting date.

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Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Present value of lessee's discounted obligation for lease payments from operating lease.

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Indicates line item in statement of financial position that includes operating lease liability.

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Amount of lessee's right to use underlying asset under operating lease.

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The cash inflow associated with the sale of equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

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Describes the periods of time over which an entity anticipates to receive utility from its property, plant and equipment (that is, the periods of time over which an entity allocates the initial cost of its property, plant and equipment).

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The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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Summary of Significant Accounting Policies (Narrative) (Details) $ / shares in Units, T in Millions	1 Months Ended		12 Months Ended
	Jan. 31, 2020 $ / shares	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) T	Dec. 31, 2018 USD ($)	Jan. 01, 2019 USD ($)
Revenue, Major Customer [Line Items]
Allowance for doubtful accounts			$ 0	$ 0
Surety bonds			27,000,000
DD&A			48,572,000	44,167,000
Revenue			323,462,000	$ 293,557,000
Right-of-use asset			800,000		$ 500,000
Operating lease liabilities			$ 800,000		$ 500,000
Operating Lease, Liability, Statement of Financial Position [Extensible List]			Other		Other
Subsequent Event [Member]
Revenue, Major Customer [Line Items]
Dividends payable, amount per share \| $ / shares	$ 0.04
Dividends payable, date of record	Jan. 31, 2020
Dividends payable, date to be paid	Feb. 14, 2020
Sales Revenue, Product Line [Member] \| Four Customers [Member]
Revenue, Major Customer [Line Items]
Percentage of revenue			70.00%	82.00%
Accounts Receivable [Member] \| Five Customers [Member]
Revenue, Major Customer [Line Items]
Percentage of revenue				77.00%
Accounts Receivable [Member] \| Three Customers [Member]
Revenue, Major Customer [Line Items]
Percentage of revenue			68.00%
Coal Supply Commitment [Member]
Revenue, Major Customer [Line Items]
Coal supply commitment \| T			22.9
Year that supply commitments end			2024
Priced coal supply commitment \| T			14.5
Minimum [Member]
Revenue, Major Customer [Line Items]
Estimated useful lives			P3Y
Minimum [Member] \| Measurement Input, Discount Rate [Member]
Revenue, Major Customer [Line Items]
ARO measurement input			5.0
Maximum [Member]
Revenue, Major Customer [Line Items]
Estimated useful lives			P25Y
Maximum [Member] \| Measurement Input, Discount Rate [Member]
Revenue, Major Customer [Line Items]
ARO measurement input			10
Savoy [Member]
Revenue, Major Customer [Line Items]
Equity method investment ownership percentage		30.60%
Proceeds from the sale of investment		$ 8,000,000
Proceeds from the sale of investment, net commissions paid			$ 7,500,000
Sunrise Energy [Member]
Revenue, Major Customer [Line Items]
Equity method investment ownership percentage			50.00%