Income Taxes - Summary of Company's Net Deferred Tax Assets (Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Intangibles, including acquired in-process research and development	$ 1,303	$ 2,035
Capitalized start-up costs	502	785
Net operating loss carryforwards	9,406	13,751
Research and development credit carryforwards	5,817	1,873
Deferred revenue	15,913	1,193
Equity-based compensation	3,248	1,940
Accruals and allowances	1,112	1,139
Gross deferred tax assets	37,301	22,716
Deferred tax asset valuation allowance	(35,372)	(20,549)
Total deferred tax assets	1,929	2,167
Deferred tax liabilities:
Fixed assets	(1,929)	(2,167)
Total deferred tax liabilities	$ (1,929)	$ (2,167)