Nature of the business and basis of presentation- Liquidity (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Nature of business and basis of presentation
Net loss	$ 12,115	$ 11,324	$ 10,217	$ 6,503	$ 23,438	$ 16,720
Accumulated deficit	$ 123,989				$ 123,989		$ 100,550