Nature of Operations and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)		3 Months Ended	12 Months Ended
	Oct. 01, 2020	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Aug. 28, 2020
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Exercisable stock options, included in the diluted EPS calculation			256,000	307,000
Effect of dilutive stock options			125,000	157,000
Anti-dilutive exercisable stock options, not included in the diluted EPS calculation			7,000	0
Net unrealized gains (losses)			$ (1,091,000)	$ 737,000
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	6,405,000	13,838,000
Net revenue			77,420,000	81,329,000
Accounts receivable related to contracts with customers		223,000	223,000	301,000
Total long-term assets		9,336,000	9,336,000	8,442,000
Proceeds from sale of investments		17,000,000.0
Transfer from marketable securities to cash equivalents at fair value				2,000,000.0
Operating lease right of use assets					$ 970,000
Operating lease liabilities		942,000	942,000
Subsequent Events
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Business Combination, Acquisition Related Costs	$ 14,400,000
New Lease Agreement [Member]
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Operating lease right of use assets		970,000	970,000
New Lease Agreement [Member] | Blaw Knox Product Line From Volvo CE [Member]
Nature Of Operations And Summary Of Significant Accounting Policies [Line Items]
Operating lease right of use assets		942,000	942,000
Operating lease liabilities		970,000	$ 970,000
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	$ 3,853,000	$ 1,918,000
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