Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2012 MMcf
Property, Plant and Equipment [Line Items]
Barrel of liquids equivalents of natural gas	0.006
Oil And Gas Unproved Properties
Property, Plant and Equipment [Line Items]
Useful lives	over the lesser of five years or the average remaining lease term
Useful life	5 years
Minimum | Gathering systems
Property, Plant and Equipment [Line Items]
Useful life	15 years
Minimum | Other property and equipment
Property, Plant and Equipment [Line Items]
Useful life	3 years
Maximum
Property, Plant and Equipment [Line Items]
Revenue collection period	60 days
Maximum | Gathering systems
Property, Plant and Equipment [Line Items]
Useful life	20 years
Maximum | Other property and equipment
Property, Plant and Equipment [Line Items]
Useful life	20 years
Certain Projects | Minimum
Property, Plant and Equipment [Line Items]
Evaluation period of future potential exploratory well for determination of economic viability	1 year