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Fair Value of Financial and Derivatives Instruments - Summary of Change in Fair Value of Commodity Derivatives (Detail) (USD $)
In Thousands, unless otherwise specified |
3 Months Ended | 9 Months Ended | ||
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Sep. 30, 2013
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Sep. 30, 2012
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Sep. 30, 2013
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Sep. 30, 2012
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| Derivatives, Fair Value [Line Items] | ||||
| (Loss)gain on commodity derivatives | $ (4,278) | $ (3,762) | $ (4,495) | $ 2,882 |
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Realized (loss) gain on commodity derivatives [Member]
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| Derivatives, Fair Value [Line Items] | ||||
| (Loss)gain on commodity derivatives | (840) | 423 | (1,247) | 300 |
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Unrealized gain (loss) on commodity derivatives [Member]
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| Derivatives, Fair Value [Line Items] | ||||
| (Loss)gain on commodity derivatives | $ (3,438) | $ (4,185) | $ (3,248) | $ 2,582 |