Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Operating Loss Carryforwards [Line Items]
Pre-tax income (loss)	$ (30,598,000)	$ (10,235,000)
Tax expense	0	0
Valuation allowance	62,900,000	56,600,000
Increase in unrecognized tax benefits	0	0
Decrease in unrecognized tax benefits	0	0
Unrecognized tax benefits, penalties	0	0
Unrecognized tax benefits, interest	0	0
Unrecognized tax benefits, accrued interest and penalties	0	0
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Pre-tax income (loss)	(27,500,000)	(8,800,000)
Tax expense	0	0
Operating loss carryforwards	276,100,000
Operating loss carryforwards subject to expiration	207,500,000
Domestic Tax Authority | Tax Year 2023
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	17,400,000
Domestic Tax Authority | Tax Year 2022
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards		9,800,000
Domestic Tax Authority | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research tax credit carryforward	5,400,000
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Tax expense	0	0
Operating loss carryforwards	7,700,000
Foreign Tax Authority | National Tax Agency, Japan
Operating Loss Carryforwards [Line Items]
Pre-tax income (loss)	(3,100,000)	(1,400,000)
Foreign Tax Authority | National Tax Agency, Japan | Transphorm Japan, Inc.
Operating Loss Carryforwards [Line Items]
Pre-tax income (loss)	(1,200,000)	(1,200,000)
Foreign Tax Authority | National Tax Agency, Japan | Transphorm Ailzu, Inc.
Operating Loss Carryforwards [Line Items]
Pre-tax income (loss)	(3,000)	(600,000)
Foreign Tax Authority | National Tax Agency, Japan | Transphorm Epi, Inc.
Operating Loss Carryforwards [Line Items]
Pre-tax income (loss)	(1,900,000)	300,000
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Tax expense		1,000
Operating loss carryforwards subject to expiration	151,600,000
State and Local Jurisdiction | Tax Year 2023
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	100,000
State and Local Jurisdiction | Tax Year 2022
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards		$ 2,600,000
State and Local Jurisdiction | Research Tax Credit Carryforward | California
Operating Loss Carryforwards [Line Items]
Research tax credit carryforward	$ 4,700,000