Aggregate Amount of Capitalized Costs Relating to Crude Oil and Natural Gas Producing Activities and Aggregate Amount of Related Accumulated Depreciation Depletion and Amortization (Detail) (USD $)	Sep. 30, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Unproven properties	$ 533,293	$ 530,539
Depreciation and impairment	(513,374)	(511,847)
Oil and gas properties, net	19,919	18,692
Change
Property, Plant and Equipment [Line Items]
Unproven properties	2,754
Depreciation and impairment	(1,527)
Oil and gas properties, net	$ 1,227