Stockholders' Equity (Deficit) (Tables)
 12 Months Ended
Dec. 31, 2021
Equity [Abstract]  
Schedule of Stockholders' Equity Note, Warrants or Rights
As of December 31, 2021, warrants to purchase up to 67,767,107 shares of the Company's common stock remain outstanding at a weighted average exercise price of $1.54 per share. These warrants are summarized below:

Type of WarrantsUnderlying Common Stock to be PurchasedExercise PriceIssue DateExercise Period
Common Warrants878 $51.24 March 30, 2012March 30, 2012 to March 30, 2022
Common Warrants1,171 $51.24 August 17, 2012August 17, 2012 to July 17, 2022
Common Warrants7,806 $3.69 June 11, 2014June 11, 2014 to June 11, 2024
Common Warrants848,674 $7.50 May 24, 2018May 24, 2018 to May 24 2025
Common Warrants182 $7.50 June 26, 2018June 26, 2018 to June 26, 2025
Common Warrants1,666,667 $6.38 April 11, 2019October 11, 2019 to April 11, 2026
Common Warrants2,777,779 $6.38 June 10, 2019December 10, 2019 to June 10, 2026
Common Warrants3,073,770 $2.44 April 24, 2020April 24, 2020 to April 24, 2025
Common Warrants2,049,180 $2.44 June 9, 2020June 9, 2020 to June 9, 2025
Common Warrants57,341,000 $1.00 May 20, 2021May 20, 2021 to May 22, 2023
Total67,767,107 
Summary of Common Stock Reserved for Future Issuance
Common stock reserved for future issuance is as follows in common equivalent shares as of December 31, 2021: 
Common stock issuable upon the exercise of stock options outstanding10,625,062 
Common stock issuable upon the exercise of common stock warrants67,767,107 
Common stock available for future issuance under the 2019 ESPP1,833,085 
Common stock available for future issuance under the Amended and Restated 2014 Plan2,701,757 
Common stock available for future issuance under the Amended Inducement Plan794,737 
Total common stock reserved for future issuance83,721,748