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Supplemental Financial Statement Information - Narrative (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
[1]
Cash and Cash Equivalents [Line Items]          
Restricted cash $ 3,354,000   $ 3,354,000   $ 3,354,000
Write-off 0 $ 0 0 $ 0  
China          
Cash and Cash Equivalents [Line Items]          
Deposits $ 3,800,000   $ 3,800,000    
[1] See Note 1 – Summary of Business and Significant Accounting Policies