Balance Sheet Components - Schedule of Accrued and Other Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Research and development expenses	$ 49,384	$ 12,530
Payroll and related expenses	17,060	9,410
Excess funds payable under grant agreements	3,467	94
Operating lease liabilities, current	3,625
Restricted stock liability		1,434
Financing lease obligation, current	265	237
Other professional and consulting expenses	2,595	1,634
Other accrued expenses	540	1,156
Total accrued and other liabilities	$ 76,936	$ 26,495