Nature of the business and basis of presentation- Liquidity (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Offering expenses									$ 1,900	$ 8,500	$ 327
Net loss	$ 17,433	$ 10,138	$ 12,115	$ 11,324	$ 4,406	$ 9,482	$ 10,217	$ 6,503	51,010	30,608	$ 21,846
Accumulated deficit	$ 151,560				$ 100,550				$ 151,560	$ 100,550
At the market offering
Shares issued (in shares)									2,928,813
Gross proceeds before discounts and commissions									$ 50,000
Net proceeds									48,100
Offering expenses									$ 1,900
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