Stock-Based Compensation - Options and RSUs (Details) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2021 shares	Sep. 30, 2021 USD ($) shares	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) item $ / shares shares	Sep. 30, 2020 USD ($)
Stock Based Compensation
Share-based compensation | $		$ 2,202	$ 1,884	$ 7,147	$ 5,665
Additional disclosures
Shares of common stock available for grant		10,403,690		10,403,690
2018 Plan
Additional disclosures
Additional shares approved	825,000
Employee stock option
Stock Based Compensation
Number of homogenous groups for purposes of determining fair values of options | item				3
Contractual term of the option				10 years
Weighted-average assumptions relating to options granted
Risk-free interest rate (as a percent)		1.10%	0.50%	1.00%	1.20%
Expected term (in years)		6 years	6 years 8 months 12 days	6 years 6 months	6 years 6 months
Dividend yield (as a percent)		0.00%	0.00%	0.00%	0.00%
Expected volatility (as a percent)		70.40%	70.50%	70.60%	66.00%
Additional disclosures
Options granted (in shares)				6,373,981
Options outstanding		30,489,827		30,489,827
Grant-date weighted-average fair value (in dollars per share) | $ / shares				$ 2.36
Options exercised during the period (in shares)				1,176,386
Employee stock option | Vesting upon achievement of corporate performance-based milestones
Additional disclosures
Options outstanding		2,018,125		2,018,125
Total unrecognized compensation costs | $		$ 4,200		$ 4,200
Employee stock option | Consultant
Stock Based Compensation
Contractual term of the option				10 years
Restricted stock units
Additional disclosures
Granted (in shares)				233,750
Weighted average fair value (in dollars per share) | $ / shares				$ 3.67
Restricted stock units | Minimum
Additional disclosures
Vesting period				1 year
Restricted stock units | Maximum
Additional disclosures
Vesting period				2 years
Share based compensation options and RSUs
Additional disclosures
Total unrecognized compensation costs | $		$ 15,500		$ 15,500
Weighted-average recognition period of unamortized compensation cost				1 year 11 months 23 days