Income Taxes - Summary of Company's Net Deferred Tax Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Intangibles, including acquired in-process research and development	$ 1,201	$ 1,303
Capitalized start-up costs	463	502
Net operating loss carryforwards	34,234	9,406
Research and development credit carryforwards	11,766	5,817
Deferred revenue	12,199	15,913
Equity-based compensation	4,064	3,248
Accruals and allowances	1,359	1,112
Gross deferred tax assets	65,286	37,301
Deferred tax asset valuation allowance	(64,046)	(35,372)
Total deferred tax assets	1,240	1,929
Deferred tax liabilities:
Fixed assets	(1,240)	(1,929)
Total deferred tax liabilities	$ (1,240)	$ (1,929)