Condensed Consolidated Balance Sheets (Parenthetical) - USD ($)	Dec. 31, 2020	Sep. 30, 2020
Marketable securities, cost	$ 90,158,000	$ 89,514,000
Accounts receivable, allowance for doubtful accounts	$ 360,000	$ 442,000
Preferred stock, par value	$ 0.10	$ 0.10
Preferred stock, shares authorized	300,000	300,000
Preferred stock, shares issued	0	0
Common Stock [Member]
Common stock, par value	$ 0.10	$ 0.10
Common stock, shares authorized	15,000,000	15,000,000
Common stock, shares issued	12,287,337	12,287,337
Common stock, shares outstanding	12,287,337	12,287,337
Class B Stock [Member]
Common stock, par value	$ 0.10	$ 0.10
Common stock, shares authorized	6,000,000	6,000,000
Common stock, shares issued	2,318,857	2,318,857
Common stock, shares outstanding	2,318,857	2,318,857