Income Taxes - Schedule of Significant Components of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets
Net operating loss carryforward	$ 19,941	$ 13,797
Research and development credits	2,049	5,060
Deferred stock compensation	4,547	4,058
Deferred revenue	210	581
Other	404	254
Total deferred tax assets	27,151	23,750
Total deferred tax liabilities
Depreciable and amortizable assets	(925)	(282)
R&D intangible assets	(5,591)	(5,591)
Total deferred tax liabilities	(6,516)	(5,873)
Less: Valuation allowance	(20,635)	(17,877)
Net deferred tax assets	$ 0	$ 0