Costs and Estimated Earnings in Excess of Billings - Costs and Estimated Earnings in Excess of Billings on Uncompleted Contracts (Detail) - USD ($)	Dec. 31, 2020	Sep. 30, 2020
Costs in Excess of Billings on Uncompleted Contracts or Programs [Abstract]
Costs incurred on uncompleted contracts	$ 12,934,000	$ 10,390,000
Estimated earnings	5,267,000	4,680,000
Costs and estimated earnings on uncompleted contracts	18,201,000	15,070,000
Billings to date	13,492,000	8,665,000
Costs and estimated earnings in excess of billings	$ 4,709,000	$ 6,405,000