Nature of the business and basis of presentation- Liquidity (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Sep. 30, 2020
Offering expenses	$ 400	$ 1,800
Net loss	17,913	$ 16,191	$ 12,115	$ 11,324	$ 34,104	$ 23,438
Accumulated deficit	$ 185,664				$ 185,664		$ 151,560
At the market offering
Shares issued (in shares)					5,769,597
Gross proceeds before discounts and commissions					$ 125,000
Net proceeds					120,900
Offering expenses					$ 4,100
Loan and Security Agreement | Term Loan
Maximum borrowing								$ 40,000
Loan and Security Agreement | Initial Term Loan
Term loan								15,000
Loan and Security Agreement | Additional Term Loan One
Term loan								15,000
Loan and Security Agreement | Additional Term Loan Two
Term loan								$ 10,000