Income taxes - Effective Tax Rate Reconciliation (Details)	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Federal tax expense	21.00%	21.00%	21.00%
State taxes, net of federal benefit	1.07%	1.17%	0.09%
Foreign rate differential	(0.12%)	(0.32%)	0.07%
Withholding taxes	(0.0078)	(0.0306)	(0.0170)
Nondeductible compensation	(5.29%)	0.00%	0.00%
Stock-based compensation	0.27%	(1.94%)	(2.77%)
Change in valuation allowance	(34.54%)	(21.16%)	(18.76%)
Research and development credits	16.87%	0.00%	0.00%
Other	0.02%	0.08%	0.07%
Effective tax rate	(1.50%)	(4.23%)	(2.00%)

Effective Income Tax Rate Reconciliation, Withholding Taxes, Percent

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to statutory income tax expense (benefit) outside of the country of domicile.

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Percentage of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to nondeductible expense for share-based payment arrangement.

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Percentage of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to expense for award under share-based payment arrangement. Excludes expense determined to be nondeductible upon grant or after for award under share-based payment arrangement.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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