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Stock-based Compensation - 2015 Inducement Award Plan (Details) - shares
6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Apr. 30, 2021
Apr. 29, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Option to purchase (shares) 797,050      
2015 Inducement Award Plan        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Possible future issuance under equity compensation plan (in shares) 250,950      
Option to purchase (shares) 158,100 17,500    
Shares authorized under the plan (in shares)     500,000 90,000