| Selected Quarterly Financial Data - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 12 Months Ended | 
|---|---|---|
| Dec. 31, 2013
 MMcf | Dec. 31, 2013
 MMcf | |
| Quarterly Financial Data [Line Items] | ||
| One-time increase in production | 2,600 | 1,900 | 
| Natural Gas | ||
| Quarterly Financial Data [Line Items] | ||
| Adjustment to depreciation, depletion, amortization and accretion | $ 7.1 | $ 5.0 | 
| Reduction in net income | $ 4.6 | $ 3.2 | 
| X | ||||||||||
| 
- Definition The adjustment to depreciation, depletion and amortization for an adjustment to production volumes. No definition available. 
 | 
| X | ||||||||||
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- Definition A one-time increase in production volume for natural gas related to an erroneous conversion of MMBtu occurring in 2011 and 2012. No definition available. 
 | 
| X | ||||||||||
| 
- Details 
 | 
| X | ||||||||||
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- Definition Adjustment to net income related to adjustments to natural gas production volumes from an erroneous conversion of MMBtu. No definition available. 
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