Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 18,792	$ 21,005
Capitalized research and development	32,029	27,540
Research and development tax credit carryforwards	3,061	1,347
Stock-based compensation	2,940	2,004
Intangible assets	7,802	8,117
Depreciation and amortization	549	472
Other deferred tax assets	1,806	2,279
Total deferred tax assets	66,979	62,764
Less: valuation allowance	(66,698)	(62,472)
Deferred Tax Assets, Net of Valuation Allowance, Total	281	292
Deferred tax liabilities:
Deductions for tax in excess of financial statements	(281)	(292)
Total deferred tax liabilities	(281)	(292)
Net deferred tax assets	$ 0	$ 0