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Fair value measurement - Assets and liabilities measured on a recurring basis (Details) - Recurring - USD ($)
$ in Thousands
Jun. 30, 2021
Dec. 31, 2020
Assets, Fair Value Disclosure [Abstract]    
Cash and cash equivalents $ 680,158 $ 247,680
Total assets 680,158 247,680
Liabilities, Fair Value Disclosure [Abstract]    
Fair value of derivative liability 2,645 2,645
Total liabilities 2,645 2,645
Fair value hierarchy Level 1    
Assets, Fair Value Disclosure [Abstract]    
Cash and cash equivalents 680,158 247,680
Total assets 680,158 247,680
Level 3    
Liabilities, Fair Value Disclosure [Abstract]    
Fair value of derivative liability 2,645 2,645
Total liabilities $ 2,645 $ 2,645