Investment in Joint Venture - Summarized financial information (Details) - USD ($) $ in Thousands	4 Months Ended	12 Months Ended
	Jul. 30, 2021	Mar. 31, 2023	Mar. 31, 2022
Variable Interest Entity [Line Items]
Current assets		$ 30,688	$ 44,794
Variable Interest Entity, Measure of Activity [Abstract]
Gross loss		(950)	11,520
Variable Interest Entity, Not Primary Beneficiary | GaNovation
Variable Interest Entity [Line Items]
Current assets		4,572	4,259
Long-term assets		6,602	3,690
Other current liabilities		5,698	3,799
Due to related parties		2	(1)
Net surplus		4,729	4,151
Variable Interest Entity, Measure of Activity [Abstract]
Sales		13,275
Gross loss		(9,174)
Net loss		(10,955)
Variable Interest Entity, Not Primary Beneficiary | Transphorm, Inc.
Variable Interest Entity [Line Items]
Due to related parties		$ 745	0
Variable Interest Entity, Not Primary Beneficiary | GaNovation/AFSW
Variable Interest Entity, Measure of Activity [Abstract]
Sales			9,109
Gross loss			(9,359)
Net loss			$ (11,967)
Variable Interest Entity, Not Primary Beneficiary | Aizu Fujitsu Semiconductor Wafer Solution Limited (AFSW)
Variable Interest Entity, Measure of Activity [Abstract]
Sales	$ 2,200
Gross loss	(3,200)
Net loss	$ (4,300)