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Stock Plans - Summary of Fair Value Assumptions of Stock Purchase Plan (Detail) - Employee Stock Purchase Plan [Member]
6 Months Ended
Jun. 30, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Expected volatility, minimum 101.00%
Expected volatility, maximum 119.00%
Risk-free interest rate 0.10%
Minimum  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Expected term (in years) 6 months
Maximum  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Expected term (in years) 2 years