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Stock-Based Compensation Plan - Narrative (Details) - USD ($)
3 Months Ended 9 Months Ended
Dec. 19, 2019
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Stock Based Compensation Plans [Line Items]          
Unamortized stock-based compensation expense for outstanding options   $ 1,600,000   $ 1,600,000  
Stock-based compensation expense   300,000 $ 100,000 600,000 $ 400,000
Aggregate intrinsic value of outstanding stock options   33,000   $ 33,000  
Weighted average vesting period       2 years 8 months 12 days  
Stock Incentive Plan 2017 [Member]          
Stock Based Compensation Plans [Line Items]          
Increase in number of shares reserved for grant 600,000        
Number of shares reserved for grant and issuance 660,000        
Expiration period (in years)       10 years  
Research and Development Expense [Member]          
Stock Based Compensation Plans [Line Items]          
Stock-based compensation expense   46,000 27,000 $ 100,000 100,000
General and Administrative Expense [Member]          
Stock Based Compensation Plans [Line Items]          
Stock-based compensation expense   $ 200,000 $ 100,000 $ 500,000 $ 400,000