Risk Concentrations (Narrative) (Details) $ in Thousands, T in Millions	12 Months Ended
Dec. 31, 2015 USD ($) T	Dec. 31, 2014 USD ($)
Concentration Risk [Line Items]
Receivables	$ 135,767	$ 232,017
Trade accounts receivable (net of allowance for doubtful accounts of $7.8 million and $0.2 million, respectively)	$ 117,405	211,506
Tons of coal sold \| T	127.6
Percentage of tons sold under long term contract	68.00%
Long term contracts percentage of company revenue	55.00%
Long-term contracts, life term, minimum	1 year
Long-term contracts, life term, maximum	5 years
Electric Utilities [Member]
Concentration Risk [Line Items]
Receivables	$ 83,800	$ 134,700
Percentage of total trade accounts receivable	72.00%	64.00%
Domestic And Foreign Steel Producers [Member]
Concentration Risk [Line Items]
Trade accounts receivable (net of allowance for doubtful accounts of $7.8 million and $0.2 million, respectively)	$ 32,800	$ 76,000
Trade receivables, percentage	28.00%	36.00%

Accounts receivables percentage of total trade

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- Definition

Goods sold during the year

+ References

No definition available.

+ Details

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- Definition

The maximum life term of a long-term sales contract.

+ References

No definition available.

+ Details

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- Definition

The minimum life term of a long-term sales contract.

+ References

No definition available.

+ Details

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- Definition

Percentage of total company revenue

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of accounts receivable net current.

+ References

No definition available.

+ Details

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- Definition

Percentage of goods sold under long term contract

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
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- Definition

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3-4)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 3
-Subparagraph a(1)
-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 4
-Article 5

+ Details

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Balance Type:	debit
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- Definition

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.

+ References

No definition available.

+ Details

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- Definition

The total amount due to the entity within one year of the balance sheet date (or one operating cycle, if longer) from outside sources, including trade accounts receivable, notes and loans receivable, as well as any other types of receivables, net of allowances established for the purpose of reducing such receivables to an amount that approximates their net realizable value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3,4)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 4
-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 3
-Subparagraph a
-Article 5

+ Details

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- Details

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- Details

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