Segment Reporting - Revenues and Percentage of Consolidated Revenues (Parenthetical) (Detail) (Maximum [Member])	12 Months Ended
Dec. 31, 2012
Maximum [Member]
Segment Reporting Information [Line Items]
Percentage of revenue for BP PLC	10.00%

Percentage of revenue generated from a single external customer that accounts for 10 percent or more of an entity's revenues.

No definition available.

Name:	us-gaap_EntityWideRevenueMajorCustomerPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration