Consolidated Statements of Shareholders' Equity - USD ($)		Total	Capital in Excess of Par Value [Member]	[1]	Retained Earnings [Member]	Common Stock [Member]		Class B Stock [Member]
Beginning balance at Sep. 30, 2014		$ 114,175,000	$ 10,090,000		$ 102,657,000	$ 1,202,000	[1]	$ 226,000	[1]
Beginning balance, shares at Sep. 30, 2014	[1]					12,015,079		2,263,857
Net income (loss)		(1,819,000)			(1,819,000)
Stock-based compensation		253,000	253,000
Stock options exercised		136,000	133,000			$ 3,000	[1]
Stock options exercised, shares	[1]					28,125
Ending balance at Sep. 30, 2015		112,745,000	10,476,000		100,838,000	$ 1,205,000	[1]	$ 226,000	[1]
Ending balance, shares at Sep. 30, 2015	[1]					12,043,204		2,263,857
Net income (loss)		7,043,000			7,043,000
Stock-based compensation		37,000	37,000
Stock options exercised		380,000	374,000			$ 6,000	[1]
Stock options exercised, shares	[1]					67,875
Ending balance at Sep. 30, 2016		120,205,000	10,887,000		107,881,000	$ 1,211,000	[1]	$ 226,000	[1]
Ending balance, shares at Sep. 30, 2016	[1]					12,111,079		2,263,857
Net income (loss)		8,418,000			8,418,000
Stock-based compensation		71,000	71,000
Stock options exercised		224,000	220,000			$ 4,000	[1]
Stock options exercised, shares	[1]					43,750
Ending balance at Sep. 30, 2017		$ 128,918,000	$ 11,178,000		$ 116,299,000	$ 1,215,000	[1]	$ 226,000	[1]
Ending balance, shares at Sep. 30, 2017	[1]					12,154,829		2,263,857

[1] 2016 and 2015 adjusted for three-for-two stock split