Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Deferred Tax Assets:
Net operating loss	$ 13,444	$ 11,823
Credit carryforwards	3,987	3,258
Deferred compensation	1,456	2,009
Uniform capitalization and inventory	1,043	1,432
Stock-based compensation	879	1,094
Reserve for accrued employee benefits	791	1,208
Warranty accrual	448	892
Accrued legal	154	435
Postretirement benefits liability	112	264
Allowance for doubtful accounts	0	14
Goodwill	54	64
Other	112	44
Deferred tax assets	22,480	22,537
Deferred Tax Liabilities:
Depreciation and amortization	(6,946)	(10,002)
Deferred tax liabilities	(6,946)	(10,002)
Less: valuation allowance	(9,597)	(8,767)
Net deferred income tax asset	$ 5,937	$ 3,768