Business Segment Information - Schedule of Business Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Segment Reporting Information [Line Items]
Net revenues	$ 17,975	$ 20,692
Operating income (loss)	1,054	1,637
Identifiable assets	104,527		$ 102,098
Operating Segments | Semiconductor
Segment Reporting Information [Line Items]
Net revenues	15,575	17,232
Operating income (loss)	2,197	2,722
Identifiable assets	55,007		51,648
Operating Segments | SiC/LED
Segment Reporting Information [Line Items]
Net revenues	2,400	2,817
Operating income (loss)	(66)	534
Identifiable assets	12,934		12,717
Non-Segment Related
Segment Reporting Information [Line Items]
Net revenues		643
Operating income (loss)	(1,077)	$ (1,619)
Identifiable assets	$ 36,586		$ 37,733