Condensed Consolidated Statements of Income - USD ($)	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Net revenue	$ 18,848,000	$ 24,118,000	$ 66,845,000	$ 78,069,000
Costs and expenses:
Production costs	14,098,000	17,702,000	47,267,000	57,800,000
Product engineering and development	881,000	781,000	2,427,000	2,239,000
Selling, general and administrative	2,471,000	2,179,000	7,135,000	7,792,000
Total costs and expenses	17,450,000	20,662,000	56,829,000	67,831,000
Operating income	1,398,000	3,456,000	10,016,000	10,238,000
Other income (expense), net:
Interest and dividend income, net of fees	567,000	399,000	1,608,000	1,075,000
Net realized and unrealized gains (losses) on marketable securities	1,090,000	(503,000)	1,147,000	(1,061,000)
Other				7,000
Other income (expense),net	1,657,000	(104,000)	2,755,000	21,000
Income before income tax expense	3,055,000	3,352,000	12,771,000	10,259,000
Income tax expense	611,000	670,000	2,554,000	1,468,000
Net income	$ 2,444,000	$ 2,682,000	$ 10,217,000	$ 8,791,000
Basic Income per Common Share:
Net income per share	$ 0.17	$ 0.19	$ 0.70	$ 0.61
Diluted Income per Common Share:
Net income per share	$ 0.17	$ 0.18	$ 0.69	$ 0.60