Receivables - Receivables (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 13,455	$ 24,847
Oil and Gas Joint Interest Billing Receivables	1,439	5,738
Allowance for bad debts	(243)	(258)
Receivables, net	13,212	24,589
Oil and gas revenue accrual receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	5,825	7,293
Receivables and accrued interest [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	4,146	6,505
Notes receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 2,045	$ 1,737
Average interest rate	11.12%	4.41%
Loan secured by real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total	$ 0	$ 3,574