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Cash Equivalents And Restricted Cash And Securities (Narrative) (Details) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Restricted Cash and Cash Equivalents Items [Line Items]      
Restricted securities $ 731,000   $ 747,000
Gross realized gains or losses on cash equivalents 0 $ 0  
Money Market Funds [Member]      
Restricted Cash and Cash Equivalents Items [Line Items]      
Restricted securities 731,000   747,000
Maturity Date Within Three Months [Member] | Money Market Funds [Member]      
Restricted Cash and Cash Equivalents Items [Line Items]      
Restricted securities $ 731,000   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