Computation of Basic and Diluted Earnings per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net loss, basic	$ (117,042)	$ (630,210)	$ (171,799)
Less: gain on common stock held by the NQDC	0	(3,184)	0
Net loss, diluted	$ (117,042)	$ (633,394)	$ (171,799)
Weighted-average common shares outstanding, basic	174,427	165,985	160,025
Common stock held by the NQDC	0	234	0
Weighted-average common shares outstanding, diluted	174,427	166,219	160,025
Net loss per common share, basic	$ (0.67)	$ (3.80)	$ (1.07)
Net loss per common share, diluted	$ (0.67)	$ (3.81)	$ (1.07)