Summary of Accounts Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Receivables [Abstract]
Customers	$ 49,978	$ 43,967
Joint interest partners	13,197	16,154
Other	2,851	4,523
Accounts Receivable, Gross, Current, Total	66,026	64,644
Less: Allowance for doubtful accounts	(1,648)	(1,666)
Accounts receivable, net of allowance for doubtful accounts	$ 64,378	$ 62,978