Going concern (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Nov. 05, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit		$ 199,174		$ 199,174		$ 159,919
Net loss		17,701	$ 6,376	39,255	$ 20,045
Net cash used in operating activities				40,140	$ 13,861
Cash and cash equivalents		$ 21,270		$ 21,270		$ 63,842
Subsequent event | Private placement
Subsequent Event [Line Items]
Consideration received on sale of stock	$ 50,000