Exploratory Well Costs (Details) - USD ($) $ in Thousands |
12 Months Ended | ||||
|---|---|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
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| Capitalized Exploratory Well Costs [Abstract] | |||||
| Balance at January 1 | $ 8,955 | $ 17,253 | $ 9,211 | ||
| Additions Pending the Determination of Proved Reserves | 6,688 | 24,640 | 32,080 | ||
| Reclassifications to Proved Properties | (5,274) | (26,659) | (15,946) | ||
| Costs Charged to Expense (1) | [1] | (10,369) | (6,279) | (8,092) | |
| Balance at December 31 | $ 0 | $ 8,955 | $ 17,253 | ||
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