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Income Taxes - Reconciliation (Details)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate    
Federal income tax (benefit) at statutory rate 21.00% 21.00%
Permanent differences (0.41%) (0.57%)
Federal research and development credits and adjustments 2.78% 2.42%
State income tax, net of federal benefit 6.03% 5.50%
Other 0.37% 0.49%
Change in valuation allowance (29.77%) (28.85%)
Effective income tax rate 0.00% 0.00%