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Income Taxes - Schedule of effective income tax rate reconciliation (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2020
Sep. 26, 2020
Jun. 27, 2020
Mar. 28, 2020
Dec. 31, 2019
Sep. 28, 2019
Jun. 29, 2019
Mar. 30, 2019
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Income Tax Disclosure [Abstract]                      
U.S. income tax at federal statutory rate                 $ (11,063) $ (2,611) $ (6,276)
State income tax, net of federal benefits                 (1,962) (2,550) (1,072)
Foreign rate differential                 (54) 0 0
Stock warrant liability                 0 2,626 0
Share-based compensation                 (21,007) (21,236) (615)
Research and development credits                 (10) (8) (6)
Return to provision and other                 0 0 29
Change in tax rates                 2,989 73 668
Other                 529 (98) 363
Change in valuation allowance                 30,650 23,813 6,910
Provision for income tax $ 2 $ 55 $ 16 $ (1) $ (12) $ 0 $ 21 $ 0 $ 72 $ 9 $ 1