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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 |  |  |  |  |

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