Estimated Useful Lives of Property Plant and Equipment (Detail)	12 Months Ended
Dec. 31, 2011 Year
Gathering systems
Useful life, minimum	15
Useful life, maximum	20
Other property and equipment
Useful life, minimum	3
Useful life, maximum	20

The maximum useful life of long-lived, physical assets used in the normal conduct of business and not intended for resale. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

No definition available.

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLifeMaximum
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration