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Derivative Instruments and Hedges - Schedule of Information About Volume and Fair Value Amounts of Derivative Instruments (Detail) (Commodity swaps, Not Designated as Hedging Instrument, USD $)
In Thousands, unless otherwise specified |
Dec. 31, 2014
MMBTU
|
Dec. 31, 2013
MMBTU
|
|---|---|---|
| Derivative [Line Items] | ||
| Notional amount | 1,876,475 | 6,652,070 |
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Prepaid expenses and other assets
|
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| Derivative [Line Items] | ||
| Fair Value Asset | 0 | 15,505 |
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Accrued liabilities
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| Derivative [Line Items] | ||
| Fair Value Liabilities | (6,268) | (4,959) |