Summary of Accounts Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Receivables [Abstract]
Customers	$ 43,967	$ 49,763
Joint interest partners	16,154	22,755
Other	4,523	1,695
Accounts Receivable, Gross, Current, Total	64,644	74,213
Less: Allowance for doubtful accounts	(1,666)	(1,781)
Accounts receivable, net of allowance for doubtful accounts	$ 62,978	$ 72,432