Nature of the business and basis of presentation- Liquidity (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Net proceeds							$ 7,558
Offering expenses	$ 900	$ 400	$ 1,800	$ 1,800
Net loss	14,678	$ 17,913	$ 16,191	10,138	$ 12,115	$ 11,324	48,782	$ 33,577
Accumulated deficit	$ 200,342						$ 200,342		$ 151,560
At the market offering
Shares issued (in shares)							6,700,497
Gross proceeds before discounts and commissions							$ 155,800
Net proceeds							150,700
Offering expenses							$ 5,100
Loan and Security Agreement | Term Loan
Maximum borrowing				40,000				40,000
Loan and Security Agreement | Initial Term Loan
Term loan				15,000				15,000
Loan and Security Agreement | Additional Term Loan One
Term loan				15,000				15,000
Loan and Security Agreement | Additional Term Loan Two
Term loan				$ 10,000				$ 10,000