Income Taxes - Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforwards	$ 44,574	$ 33,815
Research and development credits	5,287	4,944
Capitalized start-up costs/Intangibles	11	16
Accruals and reserves	2,227	1,169
Property and equipment	188	82
Stock-based compensation	568	274
Operating lease liability	1,133
Total deferred tax assets	53,988	40,300
Less: Valuation allowance	(53,126)	(40,300)
Operating lease asset	(862)
Total deferred tax liabilities	(862)	0
Net deferred tax assets	$ 0	$ 0