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Income Taxes - Reconciliation of Statutory Federal Income Tax Rate to Effective Tax Rate (Detail)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Income Tax Disclosure [Abstract]      
Tax at federal statutory tax rate 21.00% 21.00% 21.00%
State tax, net of federal benefits 1.00% 3.00% 0.00%
Change in state effected rates (2.00%) 4.00% (4.00%)
Tax credits, net 3.00% 3.00% 1.00%
Change in valuation allowance (23.00%) (30.00%) (17.00%)
Stock-based compensation 1.00% (1.00%) (1.00%)
Other (1.00%) 0.00% 0.00%
Total 0.00% 0.00% 0.00%