Subsequent Events (Narrative) (Details) - USD ($)	Apr. 27, 2017	Mar. 31, 2017
Subsequent Event [Line Items]
Borrowing capacity of securitization agreement		$ 200,000,000
Subsequent Event [Member]
Subsequent Event [Line Items]
Borrowing capacity of securitization agreement	$ 160,000,000
Term of securitization agreement	3 years
Amount of liquidity covenant	$ 175,000,000
Liquidity covenant term	60 days
Authorized amount of repurchase program	$ 300,000,000
Common shares outstanding	25,021,079
Cash dividend declared (in usd per share)	$ 0.35
Regions [Member] \| Subsequent Event [Member] \| Secured Debt [Member]
Subsequent Event [Line Items]
Percentage of liquidation value of coal inventory	85.00%
Percentage of liquidation value of parts and supplies inventory	85.00%
Percentage of clause	35.00%
Percentage of eligible cash	100.00%
Liquidity covenant terms	60 days
Regions [Member] \| Subsequent Event [Member] \| Secured Debt [Member] \| Maximum [Member]
Subsequent Event [Line Items]
Amount of liquidity covenant, minimum	$ 250,000,000
Regions [Member] \| Subsequent Event [Member] \| Secured Debt [Member] \| Minimum [Member]
Subsequent Event [Line Items]
Amount of liquidity covenant, minimum	$ 175,000,000
Regions [Member] \| Subsequent Event [Member] \| Secured Debt [Member] \| LIBOR [Member] \| Maximum [Member]
Subsequent Event [Line Items]
Basis spread on variable rate (percent)	2.50%
Regions [Member] \| Subsequent Event [Member] \| Secured Debt [Member] \| LIBOR [Member] \| Minimum [Member]
Subsequent Event [Line Items]
Basis spread on variable rate (percent)	2.25%
Regions [Member] \| Subsequent Event [Member] \| Secured Debt [Member] \| Base Rate [Member] \| Maximum [Member]
Subsequent Event [Line Items]
Basis spread on variable rate (percent)	1.50%
Regions [Member] \| Subsequent Event [Member] \| Secured Debt [Member] \| Base Rate [Member] \| Minimum [Member]
Subsequent Event [Line Items]
Basis spread on variable rate (percent)	1.25%
Revolving Credit Facility [Member] \| Subsequent Event [Member] \| Secured Debt [Member]
Subsequent Event [Line Items]
Aggregate principal amount	$ 40,000,000

Line of Credit Facility, Covenant Compliance, Borrowing Base, Percentage of Cash

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- Definition

Line of Credit Facility, Covenant Compliance, Borrowing Base, Percentage of Clause

+ References

No definition available.

+ Details

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- Definition

Line of Credit Facility, Covenant Compliance, Borrowing Base, Percentage of Coal Inventory

+ References

No definition available.

+ Details

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- Definition

Line of Credit Facility, Covenant Compliance, Borrowing Base, Percentage of Parts and Supplies Inventory

+ References

No definition available.

+ Details

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- Definition

Line of Credit, Liquidity Covenant, Amount

+ References

No definition available.

+ Details

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- Definition

Line of Credit, Liquidity Covenant, Compliance Terms, Period

+ References

No definition available.

+ Details

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- Definition

Securitization Agreement, Liquidity Covenant, Amount

+ References

No definition available.

+ Details

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- Definition

Securitization Agreement, Liquidity Covenant, Compliance Terms, Period

+ References

No definition available.

+ Details

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- Definition

Securitization Agreement, Term

+ References

No definition available.

+ Details

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- Definition

Securitization Facility, Maximum Borrowing Capacity

+ References

No definition available.

+ Details

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- Definition

Aggregate dividends declared during the period for each share of common stock outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
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- Definition

Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Paragraph 2
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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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- Definition

Amount of stock repurchase plan authorized.

+ References

No definition available.

+ Details

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- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

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