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Stockholders' Equity And Stock-Based Compensation (Non-Cash Stock-Based Compensation Expenses) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]    
Total non-cash stock-based compensation expense $ 988 $ 1,296
Research and development [Member]    
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]    
Total non-cash stock-based compensation expense 453 542
General and administrative [Member]    
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]    
Total non-cash stock-based compensation expense $ 535 $ 754