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Cash Equivalents And Restricted Securities (Narrative) (Details) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Dec. 31, 2019
Restricted Cash and Cash Equivalents Items [Line Items]          
Restricted securities $ 513,000   $ 513,000   $ 528,000
Restricted cash 11,996,000   11,996,000   2,000,000
Gross realized gains or losses on cash equivalents 0 $ 0 0 $ 0  
Money Market Funds [Member]          
Restricted Cash and Cash Equivalents Items [Line Items]          
Restricted securities 513,000   513,000   528,000
Maturity Date Within Three Months [Member] | Money Market Funds [Member]          
Restricted Cash and Cash Equivalents Items [Line Items]          
Restricted securities $ 513,000   $ 513,000   $ 528,000
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