Quarterly report pursuant to Section 13 or 15(d)

Accrued Expenses - Schedule of Accrued Expenses (Details)

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Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($)
$ in Thousands
Sep. 30, 2021
Dec. 31, 2020
Dec. 31, 2019
Payables And Accruals [Abstract]      
Accrued legal expenses $ 1,393 $ 957  
Compensation and related benefits 496 2,479  
Accrued warranty (Note 8) 195 204 $ 234
Other accrued expenses 548 507  
Total accrued expenses $ 2,632 $ 4,147