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, 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
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	6,156,000
Ending balance at Jun. 30, 2020	161,827,000	12,313,000	148,053,000	$ 1,229,000	$ 232,000
Ending balance, shares at Jun. 30, 2020				12,287,337	2,318,857
Beginning balance at Dec. 31, 2019	158,022,000	12,177,000	144,386,000	$ 1,228,000	$ 231,000
Beginning balance, shares at Dec. 31, 2019				12,277,337	2,308,857
Net income	(655,000)		(655,000)
Stock-based compensation	17,000	17,000
Ending balance at Mar. 31, 2020	157,384,000	12,194,000	143,731,000	$ 1,228,000	$ 231,000
Ending balance, shares at Mar. 31, 2020				12,277,337	2,308,857
Net income	4,322,000		4,322,000
Stock-based compensation	18,000	18,000
Stock options exercised	103,000	101,000		$ 1,000	$ 1,000
Stock options exercised, shares				10,000	10,000
Ending balance at Jun. 30, 2020	161,827,000	12,313,000	148,053,000	$ 1,229,000	$ 232,000
Ending balance, shares at Jun. 30, 2020				12,287,337	2,318,857
Beginning balance at Sep. 30, 2020	161,220,000	12,331,000	147,428,000	$ 1,229,000	$ 232,000
Beginning balance, shares at Sep. 30, 2020				12,287,337	2,318,857
Net income	1,551,000		1,551,000
Ending balance at Dec. 31, 2020	162,771,000	12,331,000	148,979,000	$ 1,229,000	$ 232,000
Ending balance, shares at Dec. 31, 2020				12,287,337	2,318,857
Beginning balance at Sep. 30, 2020	161,220,000	12,331,000	147,428,000	$ 1,229,000	$ 232,000
Beginning balance, shares at Sep. 30, 2020				12,287,337	2,318,857
Net income	6,174,000
Ending balance at Jun. 30, 2021	167,450,000	12,386,000	153,602,000	$ 1,230,000	$ 232,000
Ending balance, shares at Jun. 30, 2021				12,298,337	2,318,857
Beginning balance at Dec. 31, 2020	162,771,000	12,331,000	148,979,000	$ 1,229,000	$ 232,000
Beginning balance, shares at Dec. 31, 2020				12,287,337	2,318,857
Net income	2,288,000		2,288,000
Stock options exercised	56,000	55,000		$ 1,000
Stock options exercised, shares				11,000
Ending balance at Mar. 31, 2021	165,115,000	12,386,000	151,267,000	$ 1,230,000	$ 232,000
Ending balance, shares at Mar. 31, 2021				12,298,337	2,318,857
Net income	2,335,000		2,335,000
Ending balance at Jun. 30, 2021	$ 167,450,000	$ 12,386,000	$ 153,602,000	$ 1,230,000	$ 232,000
Ending balance, shares at Jun. 30, 2021				12,298,337	2,318,857