Organization and Summary of Significant Accounting Policies - Summary Of Changes In Future Abandonment Liabilities (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Asset Retirement Obligations [Line Items]
Asset retirement obligations at January 1	$ 62,625,000		$ 56,320,000		$ 50,167,000
Accretion expense	3,105,000		3,163,000		2,665,000
Revisions	(2,871,000)		1,947,000		2,564,000
Plus: Additions for new assets	6,679,000		3,559,000		2,794,000
Less: Plugging costs and sold assets	22,367,000	[1]	2,364,000	[1]	1,870,000	[1]
Total asset retirement obligations at December 31	47,171,000		62,625,000		56,320,000
Less: Current portion of asset retirement obligations at December 31	2,227,000		2,287,000		2,241,000
Non-current portion of asset retirement obligations at December 31	44,944,000		60,338,000		54,079,000
Asset retirement obligation disposed off	$ 20,000,000

[1] As a result of asset dispositions during the year ended December 31, 2012, the Company removed $20.0 million of its previously recognized asset retirement obligations that were assumed by the buyers. See Note 13. Property Acquisitions and Dispositions for further discussion.