| Income taxes - Loss before Income Taxes (Details) - USD ($) $ in Thousands | 12 Months Ended | ||
|---|---|---|---|
| Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | |
| Income taxes | |||
| Loss before income tax expense | $ (162,959) | $ (157,299) | $ (129,930) | 
| U.S. | |||
| Income taxes | |||
| Loss before income tax expense | (3,245) | 1,625 | (1,359) | 
| U.K. | |||
| Income taxes | |||
| Loss before income tax expense | $ (159,714) | $ (158,924) | $ (128,571) | 
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- Definition Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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- References No definition available. 
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- Details 
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