Summary of significant accounting policies - Disaggregated Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Disaggregation of Revenue [Line Items]
Revenue recognized	$ 3,860	$ 6,130	$ 8,020	$ 11,125
United states
Disaggregation of Revenue [Line Items]
Revenue recognized	2,319	3,446	4,361	5,773
Germany
Disaggregation of Revenue [Line Items]
Revenue recognized	401	636	825	965
Switzerland
Disaggregation of Revenue [Line Items]
Revenue recognized	609	1,048	1,488	2,090
All other countries
Disaggregation of Revenue [Line Items]
Revenue recognized	531	1,000	1,346	2,297
Product and service revenue - recurring
Disaggregation of Revenue [Line Items]
Revenue recognized	2,500	1,904	5,158	3,368
Product and service revenue - non-recurring
Disaggregation of Revenue [Line Items]
Revenue recognized	$ 1,360	3,790	$ 2,862	7,111
Non-commercial revenue - non-recurring
Disaggregation of Revenue [Line Items]
Revenue recognized		$ 436		$ 646