Revenue Recognition and Related Costs - Disaggregation of Company's Net Revenue by Major Source (Detail) - USD ($)	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Net revenue	$ 18,964,000	$ 18,030,000
Equipment Sales [Member] | Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Net revenue	4,132,000	12,090,000
Equipment Sales [Member] | Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Net revenue	10,136,000	1,907,000
Parts and Component Sales [Member]
Disaggregation of Revenue [Line Items]
Net revenue	3,931,000	3,146,000
Freight Revenue [Member]
Disaggregation of Revenue [Line Items]
Net revenue	745,000	903,000
Other [Member]
Disaggregation of Revenue [Line Items]
Net revenue	$ 20,000	$ (16,000)