Income Taxes - Components of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 48,182	$ 38,813
Research and development credit carryforwards	12,797	9,979
Compensation expense	1,156	1,552
Other	903	1,166
Total deferred tax assets	63,038	51,510
Valuation allowance for deferred tax assets	(63,038)	(51,510)
Net deferred tax assets	$ 0	$ 0