Summary of Accounts Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Customers	$ 49,763	$ 44,783
Joint interest partners	22,755	23,526
Other	1,695	4,442
Accounts Receivable, Gross, Current, Total	74,213	72,751
Less: Allowance for doubtful accounts	(1,781)	(373)
Accounts receivable, net of allowance for doubtful accounts	$ 72,432	$ 72,378