Condensed Consolidated Statements of Shareholders' Equity - USD ($)		Total		Capital in Excess of Par Value [Member]	Retained Earnings [Member]		Common Stock [Member]	Class B Stock [Member]
Beginning balance at Sep. 30, 2018		$ 145,017,000	[1]	$ 11,862,000	$ 131,701,000	[1]	$ 1,225,000	$ 229,000
Beginning balance, shares at Sep. 30, 2018							12,252,337	2,288,857
Net income	[1]	313,000			313,000
Stock-based compensation		17,000	[1]	17,000
Ending balance at Dec. 31, 2018		145,347,000	[1]	11,879,000	132,014,000	[1]	$ 1,225,000	$ 229,000
Ending balance, shares at Dec. 31, 2018							12,252,337	2,288,857
Beginning balance at Sep. 30, 2019		155,515,000		12,159,000	141,897,000		$ 1,228,000	$ 231,000
Beginning balance, shares at Sep. 30, 2019							12,277,337	2,308,857
Net income		2,489,000			2,489,000
Stock-based compensation		18,000		18,000
Ending balance at Dec. 31, 2019		$ 158,022,000		$ 12,177,000	$ 144,386,000		$ 1,228,000	$ 231,000
Ending balance, shares at Dec. 31, 2019							12,277,337	2,308,857

[1] The balances as of September 30, 2018 and December 31, 2018, and the amounts for the quarter ended December 31, 2018, have been adjusted to reflect the change in inventory accounting method, as described in Note 3 to the Condensed Consolidated Financial Statements.