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Reconciliation of Asset Retirement Obligations (Detail) (USD $)
In Thousands, unless otherwise specified |
12 Months Ended | |
|---|---|---|
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Dec. 31, 2013
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Dec. 31, 2012
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| Reconciliation of Changes in Asset Retirement Obligations [Line Items] | ||
| Asset retirement obligations at beginning of period | $ 19,155 | $ 16,553 |
| Additional liability incurred / acquired | 2,165 | 2,872 |
| Accretion expense | 1,327 | 1,003 |
| Liabilities settled | (1,573) | (1,273) |
| Revisions to previous estimates | 10,915 | |
| Asset retirement obligations at end of period | 31,989 | 19,155 |
| Less: current asset retirement obligations | (1,825) | (3,417) |
| Long-term asset retirement obligations | $ 30,164 | $ 15,738 |