Income Taxes - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2022	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Loss before tax expense	$ 6,579,000	$ 10,235,000	$ 17,909,000
Tax expense	0	0	0
Valuation allowance	53,500,000	56,600,000
Increase in unrecognized tax benefits	0	0	0
Decrease in unrecognized tax benefits	0	0	0
Unrecognized tax benefits, penalties	0	0	0
Unrecognized tax benefits, interest	0	0	0
Unrecognized tax benefits, accrued interest and penalties	0	0
Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research tax credit carryforward		4,300,000
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Loss before tax expense	4,900,000	(8,800,000)	10,300,000
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Tax expense	0	0	0
Operating loss carryforwards		258,900,000
Operating loss carryforwards subject to expiration		207,500,000
Domestic Tax Authority | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research tax credit carryforward		5,000,000
Domestic Tax Authority | Tax Year 2022
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards		9,800,000
Domestic Tax Authority | Tax Year 2021
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	4,500,000
Domestic Tax Authority | Tax Year 2020
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards			10,500,000
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Tax expense	1,000	1,000	1,000
Operating loss carryforwards subject to expiration		154,000,000
State and Local Jurisdiction | Tax Year 2022
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards		2,600,000
State and Local Jurisdiction | Tax Year 2021
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	1,000,000
State and Local Jurisdiction | Tax Year 2020
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards			2,600,000
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Tax expense	0	0	0
Operating loss carryforwards		6,500,000
Foreign Tax Authority | National Tax Agency, Japan
Operating Loss Carryforwards [Line Items]
Loss before tax expense	1,700,000	(1,400,000)	7,600,000
Foreign Tax Authority | National Tax Agency, Japan | Transphorm Japan, Inc.
Operating Loss Carryforwards [Line Items]
Loss before tax expense		(1,200,000)	800,000
Foreign Tax Authority | National Tax Agency, Japan | Transphorm Ailzu, Inc.
Operating Loss Carryforwards [Line Items]
Loss before tax expense	$ 1,500,000	(627,000)	6,800,000
Foreign Tax Authority | National Tax Agency, Japan | Transphorm Epi, Inc.
Operating Loss Carryforwards [Line Items]
Loss before tax expense		$ 344,000	$ (25,000)