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Stockholders' Equity - Summary of Fair Value of Purchase Right Granted Using Black-Scholes Option Pricing Model (Details) - 1997 Employee Stock Purchase Plan
6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Risk-free interest rate 0.04% 0.10%
Dividend yield 0.00% 0.00%
Volatility 48.30% 63.30%
Expected life 6 months 6 months