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Company and Summary of Significant Accounting Policies - Stock-Based Compensation (Details) - Equity Incentive 2011 Plan [Member]
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Significant Accounting Policies [Line Items]    
Expected term (in years) 6 years 6 years
Weighted average volatility (percentage) 117.97% 101.92%
Weighted average risk free interest rate (percentage) 0.70% 1.71%
Expected dividends 0.00% 0.00%
Weighted-average expected forfeiture rate (percentage) 19.64% 15.32%