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Priced coal supply commitment

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Reduction to depreciation, depletion, and amortization

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Year Supply Commitments End

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Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
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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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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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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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Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

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Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets.

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Fair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities.

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Fair value as of the balance sheet date of interest rate derivative assets, net of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized on the balance sheet.

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Number of interest rate derivative instruments held by the entity at the reporting date.

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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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Summary of Significant Accounting Policies (Narrative) (Details) $ in Thousands, T in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) agreement T	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Nov. 03, 2016	Nov. 02, 2016	Oct. 01, 2014	Sep. 30, 2014
Revenue, Major Customer [Line Items]
DD&A	$ 35,565	$ 43,942	$ 29,262
Interest swaps, net	(200)
Fair value of long term asset	300
Fair value of current liability	$ 500
Number of interest rate swaps \| agreement	2
Interest Rate Swap [Member]
Revenue, Major Customer [Line Items]
Interest swaps, net	$ (200)
Interest Rate Swap One [Member]
Revenue, Major Customer [Line Items]
Notional value of interest rate swap	125,000
Interest Rate Swap Two [Member]
Revenue, Major Customer [Line Items]
Notional value of interest rate swap	60,000
Change from Straight Line Method to Units of Production Method [Member]
Revenue, Major Customer [Line Items]
Reduction to depreciation, depletion, and amortization	$ 2,600
Sales Revenue, Goods, Net [Member] \| Five Customers [Member]
Revenue, Major Customer [Line Items]
Percentage of total revenue from largest customers	90.00%
Sales Revenue, Goods, Net [Member] \| Four Customers [Member]
Revenue, Major Customer [Line Items]
Percentage of total revenue from largest customers		82.00%	71.00%
Coal Supply Commitment [Member]
Revenue, Major Customer [Line Items]
Coal supply commitment \| T	29
Year that supply commitments end	2024
Priced coal supply commitment \| T	13
Minimum [Member]
Revenue, Major Customer [Line Items]
Discount rate	5.50%
Estimated useful lives	P3Y
Maximum [Member]
Revenue, Major Customer [Line Items]
Discount rate	10.00%
Estimated useful lives	P25Y
Savoy [Member]
Revenue, Major Customer [Line Items]
Equity method investment ownership percentage	30.60%			30.60%	40.80%	40.80%	45.00%
Sunrise Energy [Member]
Revenue, Major Customer [Line Items]
Equity method investment ownership percentage	50.00%
Carlisle Assets [Member]
Revenue, Major Customer [Line Items]
Reduction to depreciation, depletion, and amortization	$ 4,400