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, 2017	$ 128,918,000	$ 11,178,000	$ 116,299,000	$ 1,215,000	$ 226,000
Beginning balance, shares at Sep. 30, 2017				12,154,829	2,263,857
Net income	2,346,000		2,346,000
Stock-based compensation	18,000	18,000
Stock options exercised	267,000	261,000		$ 3,000	$ 3,000
Stock options exercised, shares				27,008	25,000
Ending balance at Dec. 31, 2017	131,549,000	11,457,000	118,645,000	$ 1,218,000	$ 229,000
Ending balance, shares at Dec. 31, 2017				12,181,837	2,288,857
Beginning balance at Sep. 30, 2017	128,918,000	11,178,000	116,299,000	$ 1,215,000	$ 226,000
Beginning balance, shares at Sep. 30, 2017				12,154,829	2,263,857
Net income	8,791,000
Ending balance at Jun. 30, 2018	138,145,000	11,605,000	125,091,000	$ 1,220,000	$ 229,000
Ending balance, shares at Jun. 30, 2018				12,204,837	2,288,857
Beginning balance at Dec. 31, 2017	131,549,000	11,457,000	118,645,000	$ 1,218,000	$ 229,000
Beginning balance, shares at Dec. 31, 2017				12,181,837	2,288,857
Net income	3,764,000		3,764,000
Stock-based compensation	18,000	18,000
Stock options exercised	74,000	72,000		$ 2,000
Stock options exercised, shares				15,000
Ending balance at Mar. 31, 2018	135,405,000	11,547,000	122,409,000	$ 1,220,000	$ 229,000
Ending balance, shares at Mar. 31, 2018				12,196,837	2,288,857
Net income	2,682,000		2,682,000
Stock-based compensation	18,000	18,000
Stock options exercised	40,000	40,000
Stock options exercised, shares				8,000
Ending balance at Jun. 30, 2018	138,145,000	11,605,000	125,091,000	$ 1,220,000	$ 229,000
Ending balance, shares at Jun. 30, 2018				12,204,837	2,288,857
Beginning balance at Sep. 30, 2018	142,179,000	11,862,000	128,863,000	$ 1,225,000	$ 229,000
Beginning balance, shares at Sep. 30, 2018				12,252,337	2,288,857
Net income	313,000		313,000
Stock-based compensation	17,000	17,000
Ending balance at Dec. 31, 2018	142,509,000	11,879,000	129,176,000	$ 1,225,000	$ 229,000
Ending balance, shares at Dec. 31, 2018				12,252,337	2,288,857
Beginning balance at Sep. 30, 2018	142,179,000	11,862,000	128,863,000	$ 1,225,000	$ 229,000
Beginning balance, shares at Sep. 30, 2018				12,252,337	2,288,857
Net income	10,217,000
Ending balance at Jun. 30, 2019	152,449,000	11,915,000	139,080,000	$ 1,225,000	$ 229,000
Ending balance, shares at Jun. 30, 2019				12,252,337	2,288,857
Beginning balance at Dec. 31, 2018	142,509,000	11,879,000	129,176,000	$ 1,225,000	$ 229,000
Beginning balance, shares at Dec. 31, 2018				12,252,337	2,288,857
Net income	7,460,000		7,460,000
Stock-based compensation	18,000	18,000
Ending balance at Mar. 31, 2019	149,987,000	11,897,000	136,636,000	$ 1,225,000	$ 229,000
Ending balance, shares at Mar. 31, 2019				12,252,337	2,288,857
Net income	2,444,000		2,444,000
Stock-based compensation	18,000	18,000
Ending balance at Jun. 30, 2019	$ 152,449,000	$ 11,915,000	$ 139,080,000	$ 1,225,000	$ 229,000
Ending balance, shares at Jun. 30, 2019				12,252,337	2,288,857