Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net income	$ 5,531,000	$ 10,196,000
Adjustments to reconcile net income to cash provided by operating activities:
Purchase of marketable securities	(131,635,000)	(188,066,000)
Proceeds from sale and maturity of marketable securities	146,122,000	188,047,000
Change in value of marketable securities	1,337,000	(1,245,000)
Deferred and other income taxes	(2,626,000)	732,000
Depreciation and amortization	1,643,000	1,600,000
Provision for doubtful accounts	50,000	175,000
Loss on disposal of assets		4,000
Stock-based compensation	71,000	71,000
Changes in assets and liabilities:
Accounts receivable	(439,000)	(785,000)
Costs and estimated earnings in excess of billings	7,433,000	(1,938,000)
Inventories	(1,724,000)	(3,476,000)
Prepaid expenses	(690,000)	849,000
Accounts payable	(179,000)	69,000
Customer deposits	1,935,000	(2,645,000)
Accrued expenses	(55,000)	575,000
Total adjustments	21,243,000	(6,033,000)
Cash flows provided by operating activities	26,774,000	4,163,000
Cash flows from investing activities:
Capital expenditures	(1,595,000)	(2,104,000)
Cash flows used in investing activities	(1,595,000)	(2,104,000)
Cash flows from financing activities:
Proceeds from stock option exercises	103,000	231,000
Cash flows provided by financing activities	103,000	231,000
Net increase in cash and cash equivalents	25,282,000	2,290,000
Cash and cash equivalents at:
Beginning of year	10,302,000	8,012,000
End of year	35,584,000	$ 10,302,000
Non-cash investing and financing activities:
Operating lease right-of-use assets	942,000
Operating lease liabilities	$ 942,000