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Stock-Based Compensation and warrants - Stock incentive plan and other information (Details) - USD ($) |  | 1 Months Ended | 12 Months Ended |  |  |  |  |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 05, 2019 | Mar. 20, 2007 | Dec. 31, 2020 | Dec. 31, 2019 | Nov. 16, 2020 | Nov. 15, 2020 | Sep. 17, 2020 | Oct. 31, 2018 | Oct. 10, 2018 | Sep. 24, 2018 | Sep. 07, 2017 | Aug. 25, 2016 | May 15, 2015 | Oct. 10, 2014 | Oct. 22, 2013 | Nov. 02, 2010
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options |  |  | $ 686,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from Stock Options Exercised |  |  | $ 0 | $ 0 |  |  |  |  |  |  |  |  |  |  |  |
Temporary Equity, Par or Stated Value Per Share |  |  | $ 0.001 | $ 0.001 |  |  |  |  | $ 1,000 |  |  |  |  |  |  |
Class of Warrant or Right, Outstanding |  |  |  |  |  |  |  |  | 13,672,173 |  |  |  |  |  |  |
Exercise price per warrant |  |  |  |  | $ 0.69 | $ 1.38 |  | $ 1.38 | $ 1.38 |  |  |  |  |  |  |
Common stock, par value (in dollars per share) |  |  | $ 0.001 | $ 0.001 | $ 0.001 |  |  |  |  |  |  |  |  |  |  |
General and Administrative Expenses and Research and Development Expense [Member] | Employees [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Allocated Share-based Compensation Expense |  |  | $ 213,000 | $ 295,000 |  |  |  |  |  |  |  |  |  |  |  |
Employees And Directors [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross |  |  | 1,540,000 | 1,725,000 |  |  |  |  |  |  |  |  |  |  |  |
Consultant [Member] | General and Administrative Expenses and Research and Development Expense [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Allocated Share-based Compensation Expense |  |  | $ 137,000 | $ 45,000 |  |  |  |  |  |  |  |  |  |  |  |
Employees | General and Administrative Expenses and Research and Development Expense [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Allocated Share-based Compensation Expense |  |  | $ 400,000 | $ 500,000 |  |  |  |  |  |  |  |  |  |  |  |
2007 Stock Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number |  | 71,429 | 5,145 |  |  |  |  |  |  |  |  |  |  |  |  |
2007 Stock Plan [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross |  | 7,143 |  |  |  |  |  |  |  |  |  |  |  |  |  |
2010 Stock Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number |  |  | 1,540,000 |  |  |  |  |  |  |  |  |  |  |  |  | 85,714
2010 Stock Plan [Member] | Board of Directors [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number |  |  | 2,452,273 |  |  |  |  |  |  |  |  |  |  |  |  |
2010 Stock Plan [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | 4,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock, Capital Shares Reserved for Future Issuance |  |  |  |  |  |  |  |  |  | 1,000,000 | 500,000 | 400,000 | 228,572 |  | 171,429 |
2010 Stock Plan [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross | 1,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock, Capital Shares Reserved for Future Issuance |  |  |  |  |  |  |  |  |  | 500,000 | 400,000 | 228,572 | 171,429 |  | 85,714 |
2020 Stock Plan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number |  |  |  |  |  |  | 4,000,000 |  |  |  |  |  |  |  |  |
Series A Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Warrants, Exercisable Number |  |  |  |  |  |  |  |  |  |  |  |  |  | 200,852 |  |

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