Business Segment Information - Schedule of Business Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019
Segment Reporting Information [Line Items]
Net revenues	$ 14,460	$ 20,633	$ 35,152	$ 43,858
Operating income (loss)	(972)	1,248	665	1,912
Identifiable assets	99,598		99,598		$ 126,477
Discontinued Operations
Segment Reporting Information [Line Items]
Identifiable assets					22,755
Operating Segments | Semiconductor
Segment Reporting Information [Line Items]
Net revenues	11,992	16,053	29,224	35,013
Operating income (loss)	(18)	1,732	2,704	4,477
Identifiable assets	55,337		55,337		56,855
Operating Segments | SiC/LED
Segment Reporting Information [Line Items]
Net revenues	2,468	3,273	5,285	6,256
Operating income (loss)	421	877	955	1,646
Identifiable assets	8,253		8,253		7,779
Non-Segment
Segment Reporting Information [Line Items]
Net revenues		1,307	643	2,589
Operating income (loss)	(1,375)	$ (1,361)	(2,994)	$ (4,211)
Identifiable assets	$ 36,008		$ 36,008		$ 39,088