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
	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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