Consolidated Balance Sheets (Parenthetical) - USD ($)		Sep. 30, 2017	Sep. 30, 2016
Marketable securities, cost		$ 86,967,000	$ 86,203,000
Accounts receivable, allowance for doubtful accounts		$ 207,000	$ 195,000
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	[1]	12,154,829	12,111,079
Common stock, shares outstanding	[1]	12,154,829	12,111,079
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	[1]	2,263,857	2,263,857
Common stock, shares outstanding	[1]	2,263,857	2,263,857

[1] 2016 adjusted for three-for-two stock split