Summary of Accounts Receivable (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Accounts Receivable and Major Customers [Line Items]
Customers	$ 19,221	$ 23,481
Joint interest partners	8,201	18,381
Other	7,158	7,658
Accounts Receivable, Gross, Current, Total	34,580	49,520
Less: Allowance for doubtful accounts	(2,443)	(1,555)
Accounts receivable, net of allowance for doubtful accounts	32,137	$ 47,965
Trustee [Member]
Accounts Receivable and Major Customers [Line Items]
Other	$ 4,300