Condensed Consolidated Statements of Income (Unaudited) - USD ($)	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Net revenue	$ 24,118,000	$ 23,743,000	$ 78,069,000	$ 62,052,000
Costs and expenses:
Production costs	17,702,000	17,053,000	57,800,000	44,555,000
Product engineering and development	781,000	637,000	2,239,000	1,523,000
Selling, general and administrative	2,179,000	2,259,000	7,792,000	6,576,000
Total costs and expenses	20,662,000	19,949,000	67,831,000	52,654,000
Operating income	3,456,000	3,794,000	10,238,000	9,398,000
Other income (expense), net:
Interest and dividend income, net of fees	399,000	181,000	1,075,000	384,000
Net realized and unrealized gains (losses) on marketable securities	(503,000)	(253,000)	(1,061,000)	810,000
Other			7,000
Other income (expense), net	(104,000)	(72,000)	21,000	1,194,000
Income before income tax expense	3,352,000	3,722,000	10,259,000	10,592,000
Income tax expense	670,000	1,134,000	1,468,000	3,195,000
Net income	$ 2,682,000	$ 2,588,000	$ 8,791,000	$ 7,397,000
Basic Income per Common Share:
Net income per share	$ 0.19	$ 0.18	$ 0.61	$ 0.51
Diluted Income per Common Share:
Net income per share	$ 0.18	$ 0.18	$ 0.60	$ 0.50