Income Taxes - Tax Effects of Significant Temporary Differences Representing Net Deferred Tax Asset and Liability (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Property and equipment		$ 10,536
Asset retirement obligation	$ 3,489	4,628
Net operating loss carryforwards	289,803	339,914
Alternative minimum tax carryforward	1,349	20,435
Unrealized hedging loss		2,110
Gain on debt exchange and original issue discount	4,336	16,169
Other	3,782	8,523
Noncurrent deferred tax assets	302,759	402,315
Valuation allowance on deferred tax assets	(298,539)	(398,120)
Deferred tax assets	4,220	4,195
Deferred tax liabilities:
Property and equipment	(11,878)	(9,203)
Unrealized hedging income	(277)
Other	(2,331)	(4,118)
Deferred tax liabilities	(14,486)	(13,321)
Net deferred tax liability	$ (10,266)	$ (9,126)