Income Taxes - Narratives (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating Loss Carryforwards [Line Items]
Net loss before income taxes for domestic operations	$ (68,754,000)	$ (79,483,000)
Tax provision (benefit)	0	0
Increase (decrease) in valuation allowance	(9,122,000)
Valuation allowance	43,895,000	34,773,000
Valuation allowance to be allocated to additional paid-in capital when released	1,762,000
Valuation allowance to be released through continuing operations	42,133,000
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
NOL carryforwards	174,258,000	137,909,000
NOL subject to expiration	89,051,000
NOL with an indefinite carryforward period	85,207,000
Domestic Tax Authority | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credits (“R&D credit”)	4,603,000	3,733,000
Amount federal R&D credits will expire unused	4,530,000
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
NOL carryforwards	60,206,000
State and Local Jurisdiction | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credits (“R&D credit”)	$ 1,131,000	$ 613,000