Receivables (Installment Recevables) (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Receivables [Abstract]
Non-Impaired Financing Receivable, Related Allowance	$ 0	$ 0
Installment Receivables, Current	345,000	704,000
Installment Receivables, Long-Term	909,000	1,105,000
Total Installment Receivables	1,254,000	1,809,000
Total Unearned Interest	(3,413,000)	(3,516,000)
Allowance for doubtful accounts, current	(53,000)	(325,000)
Allowance for doubtful accounts, long-term	(41,000)	(162,000)
Allowance for doubtful accounts	(94,000)	(487,000)	$ (1,514,000)
Installment receivables, net	292,000	379,000
Installment receivables, net, long-term	868,000	943,000
Installment receivables, net	$ 1,160,000	$ 1,322,000