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Summary of Business and Significant Accounting Policies - Asset Retirement Obligations Included in Other Liabilities (Detail) (USD $)
In Thousands, unless otherwise specified |
12 Months Ended | |
|---|---|---|
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Dec. 31, 2014
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Dec. 31, 2013
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| Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] | ||
| Asset retirement obligation - beginning balance | $ 13,194 | $ 11,854 |
| Adjustment to existing liabilities | (3,733) | (190) |
| Liabilities related to assets held for sale | (2,198) | 0 |
| Accretion expense | 683 | 887 |
| Settlement of existing liabilities | (262) | (903) |
| Liabilities incurred | 0 | 1,546 |
| Asset retirement obligation - ending balance | 7,968 | 13,194 |
| Less: Current portion | (453) | (486) |
| Non-current portion of asset retirement obligations, December 31 | 7,515 | 12,708 |
| Asset retirement obligation | ||
| Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] | ||
| Liabilities related to assets held for sale | $ (1,914) | $ 0 |