Condensed Consolidated Balance Sheets (Parenthetical) - USD ($)	Mar. 31, 2018	Sep. 30, 2017
Marketable securities, cost	$ 88,520,000	$ 86,967,000
Accounts receivable, allowance for doubtful accounts	$ 181,000	$ 207,000
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	12,196,837	12,154,829
Common stock, shares outstanding	12,196,837	12,154,829
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	2,288,857	2,263,857
Common stock, shares outstanding	2,288,857	2,263,857