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Summary of Significant Accounting Policies - Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Restricted Cash
Security deposit	$ 1,500	$ 1,500
Cash, Cash equivalents and restricted cash
Cash and cash equivalents	1,936,998	553,398
Restricted cash current	8,175	93,880
Restricted cash non-current	1,653	1,460
Cash, cash equivalents and restricted cash	1,946,826	648,738	$ 401,736	$ 82,180
CEPI
Restricted Cash
Restricted cash, current and non current	7,000	92,400
BMGF
Restricted Cash
Restricted cash, current and non current	$ 1,200	$ 1,500