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Commitments and Contingencies (Narrative) (Details) (USD $)
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1 Months Ended | 3 Months Ended | 1 Months Ended | 0 Months Ended | |||||
|---|---|---|---|---|---|---|---|---|---|
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Jul. 31, 2013
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Mar. 31, 2015
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Feb. 01, 2011
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Apr. 06, 2015
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Feb. 16, 2015
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Dec. 31, 2014
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Aug. 25, 2011
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May 02, 2011
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Aug. 13, 2007
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| Purchase replacement coal, excess of | $ 100,000,000 | ||||||||
| Damages and interest awarded | 104,100,000 | 104,100,000 | |||||||
| Damages and interest awarded, past damages | 13,800,000 | ||||||||
| Damages and interest awarded, future damages | 7,500,000 | 90,300,000 | |||||||
| Payments for legal settlements | 15,600,000 | ||||||||
| Settlement accrual, provision | 2,800,000 | ||||||||
| Amount accrued | 17,300,000 | 22,300,000 | |||||||
| Amount accrued current portion | 17,300,000 | 10,100,000 | |||||||
| Minimum [Member] | |||||||||
| Aggregate amount of past and future damages | 228,000,000 | ||||||||
| Maximum [Member] | |||||||||
| Aggregate amount of past and future damages | 377,000,000 | ||||||||
| Subsidiaries [Member] | Subsequent Event [Member] | |||||||||
| Litigation settlement, amount | $ (15,000,000) |