Consolidated Statements of Income - USD ($)		12 Months Ended
		Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Net revenue		$ 81,329,000	$ 98,614,000	[1]
Cost of goods sold		58,917,000	71,818,000	[1]
Gross profit		22,412,000	26,796,000	[1]
Operating expenses:
Product engineering and development		3,295,000	2,915,000	[1]
Selling, general and administrative		9,647,000	9,991,000	[1]
Total operating expenses		12,942,000	12,906,000	[1]
Operating income		9,470,000	13,890,000	[1]
Other income (expense), net:
Interest and dividend income, net of fees		2,307,000	1,535,000	[1]
Realized and unrealized gains (losses) on marketable securities, net		1,047,000	(363,000)	[1]
Other	[1]		2,000
Other income (expense),net		3,354,000	1,174,000	[1]
Income before income tax expense		12,824,000	15,064,000	[1]
Income tax expense		2,628,000	2,370,000	[1]
Net income		$ 10,196,000	$ 12,694,000	[2]
Basic earnings per common share		$ 0.70	$ 0.88	[1]
Diluted earnings per common share		$ 0.69	$ 0.86	[1]

[1] The amounts for the year ended September 30, 2018 have been adjusted to reflect the change in inventory accounting method, as described in Notes 1 and 2 to the Consolidated Financial Statements.

[2] The balances as of September 30, 2017 and 2018, and the amounts for the year ended September 30, 2018, have been adjusted to reflect the change in inventory accounting method, as described in Notes 1 and 2 to the Consolidated Financial Statements.