Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity (Stock-based Compensation Expense) (Details)

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Stockholders' Equity (Stock-based Compensation Expense) (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Share-based Compensation $ 547 $ 957 $ 1,543 $ 1,762
General and Administrative [Member]        
Share-based Compensation 240 513 564 865
Research and Development [Member]        
Share-based Compensation $ 307 $ 444 $ 979 $ 897