Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Deferred Tax Assets:
Net operating loss	$ 12,682	$ 10,823
Credit carryforwards	1,598	1,490
Deferred compensation	2,095	1,681
Uniform capitalization and inventory	1,222	1,067
Stock-based compensation	921	1,079
Reserve for accrued employee benefits	718	929
Warranty accrual	579	655
Accrued legal	130	112
Postretirement benefits liability	156	111
Other	326	379
Deferred tax assets	20,427	18,326
Deferred Tax Liabilities:
Depreciation and amortization	(4,404)	(5,035)
Retention and other	(886)	(620)
Deferred tax liabilities	(5,290)	(5,655)
Less: valuation allowance	(10,498)	(9,027)
Net deferred income tax asset	$ 4,639	$ 3,644