Oil and Gas Reserves Information (Unaudited) - Additional Information (Detail)	12 Months Ended
Dec. 31, 2017 $ / bbl $ / Mcf	Dec. 31, 2016 $ / bbl $ / Mcf
Crude Oil and NGL Per Barrel
Average Sales Price And Production Costs Per Unit Of Production [Line Items]
Average sales prices \| $ / bbl	48.71	37.62
Natural Gas Per Thousand Cubic Feet
Average Sales Price And Production Costs Per Unit Of Production [Line Items]
Average sales prices \| $ / Mcf	2.88	2.29

The revenues derived from sales of oil or gas in each geographic area during the reporting period divided by the number of barrels of oil produced or thousands of cubic feet of gas produced.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1204
-Paragraph (b)
-Subparagraph (1)

Name:	us-gaap_AverageSalesPrices
Namespace Prefix:	us-gaap_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	duration