Summary of Significant Accounting Policies - Computation of Basic and Diluted Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net (loss) income, basic	$ (42,463)	$ (2,294)
Net (loss) income, diluted	(42,463)
Loss from continuing operations	(28,808)	(4,540)
Change in fair value of warrants		12,044
Net (loss) income, diluted, continuing operations		(16,584)
Net (loss) income, basic, Discontinuing operations	$ (167)	2,246
Net (loss) income, diluted, Discontinuing operations		$ 2,246
Denominator:
Weighted average common shares outstanding	35,402	12,827
Weighted average unvested common shares subject to repurchase	(87)	(39)
Weighted average common shares outstanding - basic	35,315	12,788
Dilutive impact of warrants		494
Weighted average common shares outstanding - diluted	35,315	13,282
Basic net (loss) income per share	$ (1.20)	$ (0.18)
Diluted net (loss) income per share	(1.20)	(1.08)
Basic net (loss) income per share, Continuing operations	(0.82)	(0.36)
Diluted net (loss) income per share, Continuing operations	(0.82)	(1.25)
Basic net (loss) income per share, Discontinued operations	0.00	0.18
Diluted net (loss) income per share, Discontinued operations	$ 0.00	$ 0.17