Consolidated Income Statements - USD ($)	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net revenue	$ 98,614,000	$ 80,608,000
Cost of goods sold	71,993,000	59,449,000
Gross profit	26,621,000	21,159,000
Operating expenses:
Product engineering and development	2,915,000	2,147,000
Selling, general and administrative	9,991,000	8,776,000
Total operating expenses	12,906,000	10,923,000
Operating income	13,715,000	10,236,000
Other income (expense), net:
Interest and dividend income, net of fees	1,535,000	650,000
Realized and unrealized gains (losses) on marketable securities, net	(363,000)	1,297,000
Other	2,000	(5,000)
Other income (expense), net	1,174,000	1,942,000
Income before income tax expense	14,889,000	12,178,000
Income tax expense	2,325,000	3,760,000
Net income	$ 12,564,000	$ 8,418,000
Basic earnings per common share	$ 0.87	$ 0.58
Diluted earnings per common share	$ 0.85	$ 0.57