Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Oil and gas properties:
Proved	$ 241,308	$ 2,678,415
Unproved	8,338	6,881
Total oil and gas properties	249,646	2,685,296
Other property and equipment	3,574	31,365
Total properties and equipment	253,220	2,716,661
Accumulated depreciation, depletion and amortization	(2,020)	(2,372,266)
Property and equipment, net (successful efforts method)	$ 251,200	$ 344,395