Acquisitions and Dispositions of Oil and Gas Properties - Results of Operations for Properties (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Oil And Gas Properties Sold [Abstract]
Total oil and gas sales		$ 48,949	$ 63,303	$ 157,956
Total operating expenses	[1]	(44,861)	(80,467)	(274,651)
Operating income (loss)		$ 4,088	$ (17,164)	$ (116,695)

[1] Includes direct operating expenses, depreciation, depletion and amortization and exploration expense. Excludes interest expense, general and administrative expenses and depreciation, depletion and amortization expense subsequent to the date the assets were designated as held for sale.