Loss from Continuing Operations Before Provision for Income Tax (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
US	$ (113,679)	$ 129,361	$ (358,047)
Foreign	(3,603)	(3,697)	(10,398)
(Loss) income before income tax expense	$ (117,282)	$ 125,664	$ (368,445)