Shareholders’ equity (deficit) - Authorized share capital (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	9 Months Ended
	May 13, 2019	May 31, 2019	Sep. 30, 2019	Sep. 30, 2018	May 08, 2019
Authorized share capital
Number of shares options exercised			18,153	42,781
Average exercise price (in dollar per share)			$ 1.3225	$ 0.8298
Amount reclassified from APIC to share capital			$ (26)	$ (32)
Initial public offering | Common shares
Authorized share capital
Number of shares issued during the period	5,500,000	6,325,000
Share Price	$ 15.00	$ 15.00
Gross proceeds of initial public offering		$ 94,900
Number of preferred shares converted in to common shares		17,550,802
Options | Common shares
Authorized share capital
Number of shares issued upon exercise of options			18,153	42,781
Cash consideration			$ 25	$ 37
Number of shares options exercised			18,153	42,781
Employee Share Purchase Plan 2019 | Common shares
Authorized share capital
Number of common shares initially reserved for issuance					278,734
Percentage of shares reserved for future issuance			1.00%
Additional shares reserved for issuance			487,837
Number of shares issued under the ESPP			0