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Share-based payment, Narrative - PureTech LLC Incentive Stock (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Payment [Line Items]      
Share-based payment expense $ 10,718 $ 14,468 $ 12,637
Stock Incentive Plan [Member] | PureTech Health LLC      
Share-based Payment [Line Items]      
Share-based payment expense $ 0 $ 0 $ 200