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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 | 6 Months Ended | ||
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Jun. 30, 2013
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Jun. 30, 2012
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Jun. 30, 2013
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Jun. 30, 2012
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| Derivatives, Fair Value [Line Items] | ||||
| Gain (Loss) on commodity derivatives | $ 3,576 | $ 9,800 | $ (217) | $ 6,644 |
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Realized (Loss) Gain On Commodity Derivatives [Member]
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| Derivatives, Fair Value [Line Items] | ||||
| Gain (Loss) on commodity derivatives | (714) | 361 | (407) | (123) |
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Unrealized Gain On Commodity Derivatives [Member]
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| Derivatives, Fair Value [Line Items] | ||||
| Gain (Loss) on commodity derivatives | $ 4,290 | $ 9,439 | $ 190 | $ 6,767 |