Nature of Operations and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)			3 Months Ended		12 Months Ended
	Nov. 01, 2021	Oct. 01, 2020	Mar. 31, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Exercisable stock options, included in the diluted EPS calculation					236,000	256,000
Effect of dilutive stock options					116,000	125,000
Anti-dilutive exercisable stock options, not included in the diluted EPS calculation					0	7,000
Net unrealized gains (losses)					$ 1,302,000	$ (1,091,000)
Transfers of investments between Level 1 and Level 2				$ 0	0	0
Impairment loss recognized on an asset group					0	0
Valuation allowance				0	0	0
Costs and estimated earnings in excess of billings				6,405,000	1,903,000	6,405,000
Net revenue					85,278,000	77,420,000
Accounts receivable related to contracts with customers				223,000	210,000	223,000
Total long-term assets				9,336,000	12,639,000	9,336,000
Proceeds from sale of investments				17,000,000.0
Blawknox Paver Member [Member]
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Business Combination, Consideration Transferred		$ 14,400,000	$ 13,800,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory					10,400,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment					$ 3,400,000
Maximum [Member]
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Contract assets collection period					1 year
Current Liabilities [Member]
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Customer deposits related to contracts with customers				$ 3,853,000	$ 5,244,000	$ 3,853,000
Entities Owned by One Global Company [Member] | Revenue [Member] | Customer One [Member]
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration					10.00%	10.00%
Three to Four Years Old Inventory [Member]
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Inventory, minimum time period on the shelf, years					3 years
Inventory, maximum time period on the shelf, years					4 years
Cost basis reduction in inventory, percentage					50.00%
Four to Five Years Old Inventory [Member]
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Inventory, minimum time period on the shelf, years					4 years
Inventory, maximum time period on the shelf, years					5 years
Cost basis reduction in inventory, percentage					75.00%
Greater Than Five Years Old Inventory [Member]
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Inventory, minimum time period on the shelf, years					5 years
Inventory valuation estimate					$ 0
Common Class B [Member] | Subsequent Events | 2009 Plan[Member]
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Number of fully vested stock options issued under plan,Cancelled	30,000