Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Oil and gas properties:
Proved	$ 2,678,415	$ 3,390,482
Unproved 1	6,881	125,676
Total oil and gas properties	2,685,296	3,516,158
Other property and equipment	31,365	75,073
Total property and equipment	2,716,661	3,591,231
Accumulated depreciation, depletion and amortization 1	(2,372,266)	(1,766,133)
Property and equipment, net (successful efforts method)	$ 344,395	$ 1,825,098