Stock Incentive Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Common stock
Shares
Exercised (in shares)	(2,992)		(2,992)
Employee stock options
Shares
Outstanding, beginning of period (in shares)			227,846
Granted (in shares)			1,113,982
Assumed in Quellis Acquisition (in shares)			55,414
Exercised (in shares)		0	(2,992)	0
Cancelled or forfeited (in shares)			(58,344)
Expired (in shares)			(1,507)
Outstanding, end of period (in shares)	1,334,399		1,334,399		227,846
Vested and exercisable (in shares)	127,064		127,064
Weighted-Average Exercise Price
Outstanding, beginning of period (in dollars per share)			$ 68.25
Granted (in dollars per share)			16.21
Assumed in Quellis Acquisition (in dollars per share)			1.73
Exercised (in dollars per share)			2.10
Cancelled or forfeited (in dollars per share)			62.08
Expired (in dollars per share)			100.85
Outstanding at end of year (in dollars per share)	$ 22.43		22.43		$ 68.25
Vested and Exercisable (in dollars per share)	$ 74.71		$ 74.71
Weighted Average Remaining Contractual Term (years)
Outstanding			9 years 3 months		8 years 1 month 17 days
Vested and Exercisable			7 years 4 months 17 days
Aggregate Intrinsic Value
Outstanding	$ 374		$ 374
Vested and Exercisable	178		178
Stock Incentive Plans
Intrinsic value of options exercised	38		38
Aggregate fair value of options vested	$ 300	$ 300	$ 1,300	$ 1,000
Weighted average grant date fair value of options granted (in dollars per share)	$ 6.20	$ 29.10	$ 10.15	$ 22.32
Unrecognized compensation expense related to unvested stock option awards	$ 11,800		$ 11,800
Weighted-average amortization period over which cost is expected to be recognized			3 years 1 month 6 days