Stockholders' Equity And Stock-Based Compensation Expense (Non-Cash Stock-Based Compensation Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total non-cash stock-based compensation expense	$ 252	$ 329	$ 522	$ 673
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total non-cash stock-based compensation expense	111	135	226	272
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total non-cash stock-based compensation expense	$ 141	$ 194	$ 296	$ 401