Revenue from contracts with customers - Receivables, Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Contract assets:
Trade account receivable	$ 918	$ 421
Unbilled receivables, which are included in 'Prepaid expenses and other current assets'	41	17
Total contract assets	959	438
Contract liabilities:
Deferred revenue, current	2,595	2,665
Deferred revenue, noncurrent	20	54
Customer deposit, which are included in 'Accrued expenses and other current liabilities'	21	21
Total contract liabilities	$ 2,636	$ 2,740