Percentage of Revenue by Major Customers (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Revenue, Major Customer [Line Items]
Percentage of receipts	10.00%
ConocoPhillips
Revenue, Major Customer [Line Items]
Percentage of receipts	16.00%	[1]	16.00%	[1]	17.00%	[1]
ConocoPhillips | Companies Separated Into Two
Revenue, Major Customer [Line Items]
Percentage of receipts	8.00%
Number of companies separated	2

[1] ConocoPhillips split into two separate companies during 2012 and individually were approximately 8% each.