Income Taxes - Net Deferred Tax Assets (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating loss carryforwards	$ 63,069,000	$ 44,574,000
Research and development credits	7,191,000	5,287,000
Capitalized start-up costs/Intangibles	8,000	11,000
Accruals and reserves	2,337,000	2,227,000
Property and equipment	0	188,000
Stock-based compensation	1,859,000	568,000
Operating lease liability	935,000	1,133,000
Interest limitation	813,000	0
Total deferred tax assets	76,212,000	53,988,000
Less: Valuation allowance	(75,289,000)	(53,126,000)
Deferred tax liabilities:
Operating lease asset	(707,000)	(862,000)
Property and equipment	(216,000)	0
Total deferred tax liabilities	(923,000)	(862,000)
Net deferred tax assets	$ 0	$ 0