Condensed Consolidated Balance Sheets (Parenthetical) - USD ($)	Jun. 30, 2019	Sep. 30, 2018
Marketable securities, cost	$ 104,556,000	$ 103,751,000
Accounts receivable, allowance for doubtful accounts	$ 341,000	$ 313,000
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	12,252,337	12,252,337
Common stock, shares outstanding	12,252,337	12,252,337
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	2,288,857	2,288,857
Common stock, shares outstanding	2,288,857	2,288,857