Organization and Summary of Significant Accounting Policies - Revenue Recognition from Crude Oil and Natural Gas Sales (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenue Recognition [Line Items]
Estimated crude oil and natural gas revenues	$ 530,601	$ 491,585	$ 263,075