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Investments And Fair Value Of Financial Instruments (Fair Value Of Financial Assets Measured On A Recurring Basis) (Details) - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
ASSETS    
Total assets measured at fair value $ 17,192 $ 24,928
Cash And Cash Equivalents [Member] | Money Market Funds [Member]    
ASSETS    
Total cash and cash equivalents 7,176 6,429
Cash And Cash Equivalents [Member] | U.S. Treasury Securities [Member]    
ASSETS    
Total cash and cash equivalents 2,004  
Investments [Member] | U.S. Treasury Securities [Member]    
ASSETS    
Total investments 8,012 18,499
Level 1 [Member]    
ASSETS    
Total assets measured at fair value 7,176 6,429
Level 1 [Member] | Cash And Cash Equivalents [Member] | Money Market Funds [Member]    
ASSETS    
Total cash and cash equivalents 7,176 6,429
Level 2 [Member]    
ASSETS    
Total assets measured at fair value 10,016 18,499
Level 2 [Member] | Cash And Cash Equivalents [Member] | U.S. Treasury Securities [Member]    
ASSETS    
Total cash and cash equivalents 2,004  
Level 2 [Member] | Investments [Member] | U.S. Treasury Securities [Member]    
ASSETS    
Total investments $ 8,012 $ 18,499