Earnings per Common Share - Reconciliation of Numerators and Denominators of Basic and Diluted Earnings Per Common Share Computations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Basic:
Net (loss) income	$ (7,008)	$ (18,880)	$ (9,770)	$ (10,709)	$ (16,210)	$ (11,951)	$ (14,879)	$ 48,325	$ (15,942)	$ (15,977)	$ (16,486)	$ (18,733)	$ (33,867)	$ 5,285	$ (67,138)
Less deemed dividend related to beneficial conversion feature on Series B Preferred Stock													(12,500)
Net (loss) income attributable to common stockholders, basic													$ (46,367)	$ 5,285	$ (67,138)
Weighted average common shares outstanding													63,165,063	55,355,802	53,679,134
Basic (loss) income per common share	$ (0.13)	$ (0.29)	$ (0.16)	$ (0.18)	$ (0.31)	$ (0.21)	$ (0.27)	$ 0.89	$ (0.29)	$ (0.30)	$ (0.31)	$ (0.35)	$ (0.73)	$ 0.10	$ (1.25)
Effect of dilutive securities:
Net (loss) income attributable to common stockholders, diluted													$ (46,367)	$ 5,285	$ (67,138)
Weighted average common shares outstanding													63,165,063	55,355,802	53,679,134
Effect of dilutive options and warrants														1,046,677
Diluted weighted average common shares outstanding													63,165,063	56,402,479	53,679,134
Diluted (loss) income per common share	$ (0.13)	$ (0.29)	$ (16.00)	$ (0.18)	$ (0.30)	$ (0.21)	$ (0.27)	$ 0.87	$ (0.29)	$ (0.30)	$ (0.31)	$ (0.35)	$ (0.73)	$ 0.09	$ (1.25)