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Cash Equivalents And Restricted Cash And Securities (Narrative) (Details) - USD ($)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Restricted Cash and Cash Equivalents Items [Line Items]      
Restricted securities $ 528,000 $ 747,000  
Gross realized gains or losses on cash equivalents 0 0 $ 0
Money Market Funds [Member]      
Restricted Cash and Cash Equivalents Items [Line Items]      
Restricted securities 528,000 747,000  
Maturity Date Within Three Months [Member] | Money Market Funds [Member]      
Restricted Cash and Cash Equivalents Items [Line Items]      
Restricted securities $ 528,000 512,000  
Maturity Date Between Three Months And One Year [Member] | Money Market Funds [Member]      
Restricted Cash and Cash Equivalents Items [Line Items]      
Restricted securities   $ 235,000  
Minimum [Member] | Maturity Date Between Three Months And One Year [Member] | Money Market Funds [Member] | Measurement Input, Expected Term [Member]      
Restricted Cash and Cash Equivalents Items [Line Items]      
Restricted securities maturity period   3 months  
Maximum [Member] | Maturity Date Within Three Months [Member] | Money Market Funds [Member] | Measurement Input, Expected Term [Member]      
Restricted Cash and Cash Equivalents Items [Line Items]      
Restricted securities maturity period 3 months 3 months  
Maximum [Member] | Maturity Date Between Three Months And One Year [Member] | Money Market Funds [Member] | Measurement Input, Expected Term [Member]      
Restricted Cash and Cash Equivalents Items [Line Items]      
Restricted securities maturity period   1 year