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Stockholders' Equity - Stock Option Assumptions (Details) - Equity Incentive 2011 Plan [Member] - $ / shares
3 Months Ended 12 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total stock options granted 8,917 30,542 586,552
Weighted average exercise price, granted $ 0.25 $ 1.46 $ 0.67
Weighted-average expected term (in years) 6 years 6 years  
Weighted average volatility (percentage) 101.92% 63.37%  
Weighted average risk free interest rate (percentage) 1.71% 2.52%  
Weighted average grant date fair value, granted $ 0.16 $ 0.91 $ 0.40