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Nature of the business and basis of presentation - Initial public offering (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	12 Months Ended
	May 28, 2019	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share capital reorganization and share split
Offering expenses			$ 1,900	$ 8,500	$ 327
Ordinary Shares
Share capital reorganization and share split
Shares issued (in shares)			2,928,813	4,637,666
IPO
Share capital reorganization and share split
Shares issued (in shares)	4,333,333
Share issue price	$ 14.00
Proceeds from IPO, net			$ 56,400
Underwriting discounts and commissions			4,500
Offering expenses			$ 4,000
Over allotment option
Share capital reorganization and share split
Shares issued (in shares)		304,333
Shares sold (in shares)		304,333
At the market offering
Share capital reorganization and share split
Shares issued (in shares)			2,928,813
Offering expenses			$ 1,900