Consolidated Statements of Cash Flows Supplemental Disclosures (Non-cash Investing and Financing Activities) (Details) - USD ($) $ in Thousands |
6 Months Ended | |
|---|---|---|
Jun. 30, 2017 |
Jun. 30, 2016 |
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| Supplemental Cash Flow Elements [Abstract] | ||
| Non-cash additions for purchases of property and equipment | $ 17,226 | $ 15,878 |
| Net asset retirement obligation additions to property and equipment | $ 978 | $ 769 |
| X | ||||||||||
- Definition Future cash outflow to pay for purchases of fixed assets that have occurred. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
- Definition The increase (decrease) during the reporting period in the carrying amount of asset retirement obligations. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
- References No definition available.
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