Asset Retirement Obligations (Details) $ in Thousands |
9 Months Ended |
|---|---|
|
Sep. 30, 2017
USD ($)
| |
| Asset Retirement Obligation, Roll Forward Analysis [Roll Forward] | |
| Asset retirement obligations at January 1, 2017 | $ 7,226 |
| Additional liabilities incurred | 1,813 |
| Liabilities settled | (65) |
| Accretion expense | 376 |
| Revision to estimated cash flows | (22) |
| Asset retirement obligations at September 30, 2017 | $ 9,328 |