Income Taxes - Summary of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Noncurrent deferred tax assets:
Stock-based compensation	$ 2,281	$ 2,216
Inventory	0	375
Accrued expenses and other	795	637
Research credit carryforward	6,182	5,540
Fixed assets	392	450
Capitalized start-up costs and other intangibles	1,859	2,130
Net operating loss carryforwards	74,566	64,300
Deferred Tax Assets, Gross	86,075	75,648
Valuation allowance	(81,337)	(71,520)
Net noncurrent deferred tax asset	4,738	4,128
Noncurrent deferred tax liabilities
Fixed assets	(686)	(334)
Purchase accounting intangibles	(8,772)	(12,183)
Net noncurrent deferred tax liability	(9,458)	(12,517)
Net deferred tax asset (liability)	$ (4,720)	$ (8,389)