Nature of the business and basis of presentation- Liquidity (Details) - USD ($) $ in Thousands		3 Months Ended						9 Months Ended
	Jun. 05, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Net loss		$ 10,138	$ 12,115	$ 11,324	$ 9,482	$ 10,217	$ 6,503	$ 33,577	$ 26,202
Accumulated deficit		134,127						$ 134,127		$ 100,550
Offering expenses		1,800				$ 8,400
At the market offering
Maximum aggregate offering price	$ 50,000
Shares issued (in shares)								2,830,713
Gross proceeds before discounts and commissions								$ 48,100
Net proceeds								46,300
Offering expenses								1,800
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