Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Valuation allowance increase (decrease)	$ (17,967,000)	$ 24,264,000	$ 8,192,000
NOL carryforward, decrease	1,506,000
Net loss	(18,527,000)	(80,805,000)	(41,978,000)
Unrecognized tax benefits that would impact effective tax rate		0
Unrecognized tax benefits	3,105,000	2,159,000	1,663,000
Unrecognized tax benefits, income tax penalties and interest accrued		0
Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	12,422,000	8,638,000
Research and development credits, decrease	32,000
Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforward	227,751,000	195,133,000
Increase (decrease) in operating loss carryforwards	142,420,000
Net loss	(17,582,000)	(79,518,000)	(41,978,000)
Foreign
Operating Loss Carryforwards [Line Items]
Operating loss carryforward	2,050,000	1,212,000
Net loss	$ (945,000)	$ (1,287,000)	$ 0