v3.8.0.1

Disclosures About Oil and Gas Producing Activities - Commodity Prices Inclusive of Adjustments for Quality and Location Used in Determining Future Net Revenues Related to Standardized Measure Calculation (Detail) - Reserve Estimate [Member] | 12 Months Ended
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Dec. 31, 2017 $ / bbl $ / Mcf | Dec. 31, 2016 $ / bbl $ / Mcf | Dec. 31, 2015 $ / bbl $ / Mcf
Oil (MBbls) [Member] |  |  |
Average Sales Price and Production Costs Per Unit of Production [Line Items] |  |  |
Commodity Prices | 51.34 | 42.69 | 50.16
NGLs (MBbls) [Member] |  |  |
Average Sales Price and Production Costs Per Unit of Production [Line Items] |  |  |
Commodity Prices | 18.67 | 14.12 | 15.13
Natural Gas (MMcf) [Member] |  |  |
Average Sales Price and Production Costs Per Unit of Production [Line Items] |  |  |
Commodity Prices | $ / Mcf | 2.99 | 2.47 | 2.64

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