Asset Retirement Obligation (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
|
| Asset Retirement Obligation Disclosure [Abstract] | |||
| Asset retirement obligation, beginning of year | $ 5,557 | $ 6,063 | $ 6,963 |
| Liabilities incurred during period | 302 | 305 | 3,416 |
| Liabilities settled during period | (37) | (704) | (126) |
| Accretion of asset retirement obligation | 502 | 506 | 468 |
| Revision in previous estimates and other | 178 | 32 | 60 |
| Deletions related to property disposals | (416) | (645) | (4,718) |
| Asset retirement obligation, end of year | $ 6,086 | $ 5,557 | $ 6,063 |