Cash Equivalents And Restricted Securities (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted securities	$ 538,000		$ 538,000		$ 546,000
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	538,000		538,000		546,000
Maturity Date Within Three Months [Member] | Money Market Funds [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted securities	$ 538,000		$ 538,000		$ 546,000
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