Investment in Joint Venture - Summarized financial information (Details) - USD ($) $ in Thousands	2 Months Ended	3 Months Ended		6 Months Ended
	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Mar. 31, 2022
Variable Interest Entity [Line Items]
Current assets		$ 46,647		$ 46,647		$ 44,794
Variable Interest Entity, Measure of Activity [Abstract]
Gross loss		438	$ 9,064	1,544	$ 9,713
Variable Interest Entity, Not Primary Beneficiary | GaNovation
Variable Interest Entity [Line Items]
Current assets		2,370		2,370		4,259
Long-term assets		4,994		4,994		3,690
Due from Transphorm		160		160		0
Other current liabilities		5,015		5,015		3,799
Due to controlling owner		12		12		(1)
Net surplus		2,497		2,497		$ 4,151
Variable Interest Entity, Measure of Activity [Abstract]
Sales	$ 1,500	3,211	2,265	6,032	3,695
Gross loss	(1,600)	(2,211)	(2,357)	(4,248)	(4,756)
Net loss	$ (2,000)	$ (2,703)	$ (3,196)	$ (5,154)	$ (6,237)