Supplemental Oil And Natural Gas Information - Additional Information (Detail) - Bcfe	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Extractive Industries [Abstract]
Extension and discoveries	196.1	221.7	323.1
Discount rate	10.00%

Energy measure of increase in quantity of proved reserve of oil and gas resulting from the extension of the proved acreage of previously discovered reservoir or discovery of new field with proved reserve or of new reservoir of proved reserve in old field, stated in a unit of energy. For example, but not limited to, barrel of oil equivalents (BOE) or one thousand cubic feet of natural gas equivalent (Mcfe).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 5
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61831-109447

Name:	us-gaap_ProvedDevelopedAndUndevelopedReserveExtensionAndDiscoveryEnergy
Namespace Prefix:	us-gaap_
Data Type:	num:energyItemType
Balance Type:	na
Period Type:	duration