Related Party Transactions [Abstract] Private Placement Private Placement [Member] Net deficit Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Valuation allowance Deferred Tax Assets, Valuation Allowance Foreign currency translation adjustments Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent Interest expense accrued Fair Value, Measurement With Unobservable Inputs Reconciliation, Recurring Basis, Liability, Interest Payable Fair Value, Measurement With Unobservable Inputs Reconciliation, Recurring Basis, Liability, Interest Expense Accrued Other Assets Other Assets [Member] Level 3 Fair Value, Inputs, Level 3 [Member] Outstanding balance on line of credit facility Long-term Line of Credit License fees Proceeds from License Fees Received Beginning balance Ending balance Noncontrolling Interest in Variable Interest Entity Foreign Currency Risk Foreign Currency Transactions and Translations Policy [Policy Text Block] Convertible preferred stock, dividend rate Temporary Equity, Convertible Preferred Stock, Dividend Rate Temporary Equity, Convertible Preferred Stock, Dividend Rate 2020 Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months Recognition of contractual income Contract with Customer, Liability, Revenue Recognized Total current liabilities Liabilities, Current National Tax Agency, Japan National Tax Agency, Japan [Member] Capitalized interest cost Interest Costs Capitalized Development loan Notes Payable, Current Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Other assets Increase (Decrease) in Other Noncurrent Assets Accounts receivable due from related party Accounts Receivable, Related Parties Increase in valuation allowance Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount Concentration Risk [Line Items] Concentration Risk [Line Items] Recently Issued Accounting Standards Adopted and under Evaluation New Accounting Pronouncements, Policy [Policy Text Block] Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] Tax Year 2019 Tax Year 2019 [Member] Proceeds from issuance of common stock, net of offering cost Proceeds from Issuance of Common Stock Sales Revenues Changes in fair value of promissory notes Changes in fair value of promissory note Fair Value, Option, Changes in Fair Value, Gain (Loss) Entity Address, Postal Zip Code Entity Address, Postal Zip Code Unfunded commitment Purchase Commitment, Remaining Minimum Amount Committed Shares issued under company plans (in shares) Options outstanding under The 2020 Plan (in shares) Beginning balance, options outstanding (in shares) Ending balance, Options outstanding (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Issuance of common stock, net Stock Issued During Period, Value, New Issues Revolving loan Line of Credit Facility, Maximum Borrowing Capacity Property and equipment, net Property, Plant and Equipment, Net, Total Property, Plant and Equipment, Net Convertible Preferred Stock Temporary Equity [Text Block] Temporary Equity Equity Method Investments Equity Method Investments [Policy Text Block] 2021 Operating Leases, Future Minimum Payments, Due in Two Years Accumulated Other Comprehensive (Loss) Income AOCI Attributable to Parent [Member] Total assets Assets Preferred stock liquidation value Preferred Stock, Liquidation Preference, Value Valuation allowance Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent Options exercised (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Cover [Abstract] Options exercisable, weighted average remaining contractual term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term The 2007 Plan The 2007 Plan [Member] The 2007 Plan Document Type Document Type Additional financial support provided to investment Investment Variable Interest Entity, Financial or Other Support, Amount Series 1 Preferred Stock Series 1 Preferred Stock [Member] Series 1 Preferred Stock Subsequent Event Subsequent Event [Member] Impairment of intangible assets Impairment of Intangible Assets, Finite-lived SCI Note SCI Note [Member] SCI Note Schedule of future minimum operating lease commitments Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Scenario [Domain] Scenario [Domain] Construction in Progress [Member] Construction in Progress [Member] Operating loss carryforwards subject to expiration Operating Loss Carryforwards Subject To Expiration Operating Loss Carryforwards Subject To Expiration Convertible preferred stock, shares issued (in shares) Temporary Equity, Shares Issued Share-based Payment Arrangement [Abstract] General and administrative General and Administrative Expense [Member] Ownership percentage in entity Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage Accounts receivable Increase (Decrease) in Accounts Receivable Current liabilities: Liabilities, Current [Abstract] Accrued interest on promissory note Interest Payable Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Estimated time of regulatory approval, maximum Estimated Time Of Regulatory Approval, Maximum Estimated Time Of Regulatory Approval, Maximum Inventory Inventory, Policy [Policy Text Block] Effect of foreign exchange rate changes on cash and cash equivalents Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Equity [Abstract] Options cancelled (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period Preferred stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding February 2025 Expiration Date 3 [Member] Expiration Date 3 Income Tax Authority [Domain] Income Tax Authority [Domain] Commitments and contingencies (Note 8) Commitments and Contingencies Cash and cash equivalents at beginning of year Cash and cash equivalents at end of year Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Weighted average common shares outstanding - basic and diluted Weighted Average Number of Shares Outstanding, Basic and Diluted Class of Stock [Domain] Class of Stock [Domain] Exercise price (in usd per share) Class of Warrant or Right, Exercise Price of Warrants or Rights Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Exercisable at period end (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Risks and Uncertainties [Abstract] Price per share (in dollars per share) Sale of Stock, Price Per Share Award vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Developed technology - 600V Developed Technology - 600V [Member] Developed Technology - 600V Conversion rate for options and warrants Conversion Rate, Options And Warrants Conversion Rate, Options And Warrants Schedules of concentration of risk, by risk factor Schedules of Concentration of Risk, by Risk Factor [Table Text Block] Other comprehensive (loss) income, net of tax Other comprehensive income Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Foreign Tax Authority Foreign Tax Authority [Member] Preferred stock outstanding Preferred Stock, Value, Outstanding Research tax credit carryforward Tax Credit Carryforward, Amount Schedule of Deferred Tax Assets and Liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Merger conversion rate (in shares) Common Stock, Merger Conversion Rate Of Shares Common Stock, Merger Conversion Rate Of Shares Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Variable Interest Entities Schedule of Variable Interest Entities [Table Text Block] Loss from operations Operating Income (Loss) Yaskawa Yaskawa [Member] Yaskawa Goodwill Goodwill Machinery and Equipment [Member] Machinery and Equipment [Member] Measurement Frequency [Domain] Measurement Frequency [Domain] Statement [Line Items] Statement [Line Items] Revenue, net Revenue from Contract with Customer, Excluding Assessed Tax Transphorm Technology 2007 Stock Plan and 2015 Equity Incentive Plan Transphorm Technology 2007 Stock Plan and 2015 Equity Incentive Plan [Member] Transphorm Technology 2007 Stock Plan and 2015 Equity Incentive Plan Goodwill and Intangible Assets Disclosure [Abstract] Lower limit of estimated enterprise value Debt Instrument, Qualified Financing, Limit Of Estimated Enterprise Value, Minimum Debt Instrument, Qualified Financing, Limit Of Estimated Enterprise Value, Minimum Other Comprehensive Income (Loss), Net of Tax [Abstract] Other Comprehensive Income (Loss), Net of Tax [Abstract] Fair Value Disclosures [Abstract] Restatement Adjustment Restatement Adjustment [Member] Inventory Inventory Disclosure [Text Block] Restatement [Domain] Restatement [Domain] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Beginning of period (in usd per share) End of period (in usd per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Cost reimbursable sub award Research and Development Arrangement with Federal Government, Customer Funding to Offset Costs Incurred Loss Per Share Earnings Per Share, Policy [Policy Text Block] Comprehensive loss Comprehensive Income (Loss), Net of Tax, Attributable to Parent Plan Name [Axis] Plan Name [Axis] Stock-based compensation APIC, Share-based Payment Arrangement, Option, Increase for Cost Recognition Subsequent Event Type [Axis] Subsequent Event Type [Axis] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Statement of Stockholders' Equity [Abstract] Revolving credit facility, including accrued interest Line of Credit, Current Amendment Flag Amendment Flag Tranche C Note Tranche C Note [Member] Tranche C Note Loan and Security Agreement (LSA) Loan And Security Agreement (LSA) [Member] Loan And Security Agreement (LSA) Schedule of Finite-Lived Intangible Assets Schedule of Finite-Lived Intangible Assets [Table Text Block] Customer B Customer B [Member] Customer B Weighted Average Exercise Price per Share Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] Total common and preferred stock authorized for issuance (in shares) Capital Units, Authorized Beginning balance (in shares) Ending balance (in shares) Common stock outstanding (in shares) Common Stock, Shares, Outstanding Customer [Axis] Customer [Axis] Level 1 Fair Value, Inputs, Level 1 [Member] Tax Period [Axis] Tax Period [Axis] Interest expense Interest expense Interest Expense Unrecognized stock-based compensation Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount Total Operating Leases, Future Minimum Payments Due Class of Stock [Axis] Class of Stock [Axis] Stockholders' Equity Stockholders' Equity Note Disclosure [Text Block] Plan Name [Domain] Plan Name [Domain] Interest Expense Interest Expense [Member] Use of Estimates Use of Estimates, Policy [Policy Text Block] Business and Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Beginning Balance Ending Balance Stockholders' Equity Attributable To Parent Including Merger Adjustments Stockholders' Equity Attributable To Parent Including Merger Adjustments Inventory write-off Inventory Write-down Loss in joint venture Income (Loss) from Equity Method Investments Local Phone Number Local Phone Number Nondeductible expenses Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Proceeds from issuance of development loans Proceeds from Notes Payable Property, Plant and Equipment Property, Plant and Equipment [Table Text Block] Cash included in other assets Cash Property, Plant and Equipment [Abstract] Additional paid-in capital Additional Paid in Capital Finished goods Inventory, Finished Goods, Net of Reserves Work in process Inventory, Work in Process, Net of Reserves Options cancelled (in usd per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price Stock-based compensation expense Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Table] Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Table] Convertible preferred stock, par value (in usd per share) Temporary Equity, Par or Stated Value Per Share Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Options granted Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Stock options exercised (in shares) Options exercised (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Research Tax Credit Carryforward Research Tax Credit Carryforward [Member] Total current assets Assets, Current Assets, Current Net decrease in cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Net loss Net loss Net Income (Loss) Attributable to Parent Proceeds from stock option exercise Proceeds from Stock Options Exercised Common Stock Common Stock [Member] Current assets: Assets, Current [Abstract] Increase in fair value Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss) Thereafter Finite-Lived Intangible Assets, Amortization Expense, After Year Four Finite-Lived Intangible Assets, Amortization Expense, After Year Four Leases [Abstract] Debt Instrument [Axis] Debt Instrument [Axis] Accounts receivable, net, including related parties Receivables, Net, Current Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Customer C Customer E [Member] Customer E Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Net loss Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Number of shares (in shares) Class of Warrant or Right, Outstanding Tax Credit Carryforward [Axis] Tax Credit Carryforward [Axis] Entity Small Business Entity Small Business Commitments and Contingencies Disclosure [Abstract] Scenario [Axis] Scenario [Axis] IIDA Note IIDA Note [Member] IIDA Note Entity Filer Category Entity Filer Category Corporate Joint Venture Corporate Joint Venture [Member] Total deferred tax liabilities Deferred Tax Liabilities, Gross California capitalized research and development Deferred Tax Assets, in Process Research and Development Stock based compensation expense Share-based Payment Arrangement, Expense Customer D Customer F [Member] Customer F Related Party Transaction [Domain] Related Party Transaction [Domain] Total liabilities, convertible preferred stock and stockholders’ deficit Liabilities and Equity Transphorm Technology Transphorm Technology [Member] Transphorm Technology Conversion of shares in connection with the Reverse Merger (in shares) Share conversion in connection with the Merger (in shares) Stock Issued During Period, Shares, Conversion of Convertible Securities Entity Address, City or Town Entity Address, City or Town Income Tax Disclosure [Abstract] Percentage of revenue or accounts receivable Concentration Risk, Percentage Operating expenses: Operating Expenses [Abstract] Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized Tax Credit Carryforward, Name [Domain] Tax Credit Carryforward, Name [Domain] Purchase of additional interest Variable Interest Entity, Additional Purchase of Ownership Interest, Percentage Variable Interest Entity, Additional Purchase of Ownership Interest, Percentage Aggregate gross proceeds from closing of offering Sale of Stock, Consideration Received on Transaction Principles of Consolidation Consolidation, Policy [Policy Text Block] Stockholders’ deficit: Stockholders' Equity Attributable to Parent [Abstract] Number of shares sold in private placement offering (in shares) Sale of Stock, Number of Shares Issued in Transaction Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Concentrations of Risk Concentration Risk, Credit Risk, Policy [Policy Text Block] Deferred tax liabilities: Deferred Tax Liabilities, Deferred Expense [Abstract] 401(k) Savings Plan Pension and Other Postretirement Benefits Disclosure [Text Block] Subsequent Events Subsequent Events [Text Block] Schedule of fair value option Fair Value Option, Disclosures [Table Text Block] Estimated useful life (in years) Finite-Lived Intangible Asset, Useful Life Series 2 Preferred Stock Series 2 Preferred Stock [Member] Series 2 Preferred Stock Federal statutory income tax rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Concentration of Credit Risk and Significant Customers Concentration Risk Disclosure [Text Block] Loss in joint venture Effective Income Tax Rate Reconciliation, Loss On Joint Venture, Percent Effective Income Tax Rate Reconciliation, Loss On Joint Venture, Percent Income Tax Authority, Name [Domain] Income Tax Authority, Name [Domain] Fair Value, Recurring Fair Value, Recurring [Member] Operating loss carryforwards Operating Loss Carryforwards Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] Award Type [Axis] Award Type [Axis] Proceeds from qualified financing Proceeds From Issuance of Qualified Funding, Gross Proceeds From Issuance of Qualified Funding, Gross Cost of goods sold Cost of Revenue Other income, net Other Nonoperating Income (Expense) Class of Stock [Line Items] Class of Stock [Line Items] Subsequent Events [Abstract] Related Party Transactions Related Party Transactions Disclosure [Text Block] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Shares redeemed Stock Repurchased During Period, Value Line of Credit Facility [Table] Line of Credit Facility [Table] Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Geographical [Axis] Geographical [Axis] Issuance of preferred stock Temporary Equity, Stock Issued During Period, Value, New Issues Accumulated Deficit Retained Earnings [Member] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward] Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward] Subsequent Event [Line Items] Subsequent Event [Line Items] Liabilities, convertible preferred stock and stockholders’ deficit Liabilities [Abstract] Statement [Table] Statement [Table] Entity Registrant Name Entity Registrant Name Reimbursement from payroll related costs Employee Wages and Benefit Expense [Member] Employee Wages and Benefit Expense Property and equipment, estimated useful life Estimated Useful Life (in years) Property, Plant and Equipment, Useful Life Yaskawa Note Yaskawa Note [Member] Yaskawa Note Deferred revenue License fee Contract with Customer, Liability Operating Loss Carryforwards [Line Items] Operating Loss Carryforwards [Line Items] Liabilities measured at fair value by level Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Cash flows from investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Number of shares authorized by 2020 plan (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Maximum Maximum [Member] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] Loss before tax expense Loss before tax expense Income (Loss) Attributable to Parent, before Tax Collaborative Arrangement and Arrangement Other than Collaborative [Table] Collaborative Arrangement and Arrangement Other than Collaborative [Table] Other Investors Other Investors [Member] Other Investors Related Party [Domain] Related Party [Domain] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table] Summary of Variable Interest Entities [Roll Forward] Summary of Variable Interest Entities [Roll Forward] Summary of Variable Interest Entities Options outstanding, weighted average remaining contractual term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Ownership [Axis] Ownership [Axis] Domestic Tax Authority Domestic Tax Authority [Member] Total convertible preferred stock Temporary Equity, Carrying Amount, Attributable to Parent Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Accumulated deficit Retained Earnings (Accumulated Deficit) Convertible Preferred Stock Convertible Preferred Stock [Member] Payment for repurchase of common stock Payments for Repurchase of Common Stock Entity Tax Identification Number Entity Tax Identification Number Reimbursement for research and development Reimbursement Of Research and Development Expense [Member] Reimbursement Of Research and Development Expense Intangible Assets Intangible Assets Disclosure [Text Block] Long-term loan facility Debt Instrument, Face Amount Number of reportable segments Number of Reportable Segments Class of Warrant or Right [Axis] Class of Warrant or Right [Axis] Sales and marketing Selling and Marketing Expense Noncontrolling Common Stockholder And Noteholder Noncontrolling Common Stockholder And Noteholder [Member] Noncontrolling Common Stockholder And Noteholder Minimum Minimum [Member] Comprehensive Loss Comprehensive Income, Policy [Policy Text Block] Accounts Receivable Accounts Receivable [Policy Text Block] Principal and interest expense paid Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements 2021 Finite-Lived Intangible Assets, Amortization Expense, Year Two Raw materials Inventory, Raw Materials, Net of Reserves Balance Sheet Location [Domain] Balance Sheet Location [Domain] Legal Entity [Axis] Legal Entity [Axis] Letter of intent for development activities Collaborative Arrangement, Counterparty Funding Commitment Collaborative Arrangement, Counterparty Funding Commitment Statistical Measurement [Domain] Statistical Measurement [Domain] Adjustments to reconcile net loss to net cash used in operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Schedule of stock option activity Share-based Payment Arrangement, Option, Activity [Table Text Block] Previously Reported Previously Reported [Member] Promissory note Other Notes Payable, Noncurrent Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Accounts payable to related party Accounts Payable, Related Parties Options exercisable, aggregate intrinsic value Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Dividend yield Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Entity [Domain] Entity [Domain] Inventory Disclosure [Abstract] Tax expense Income Tax Expense (Benefit) Stock Option Plans Share-based Payment Arrangement [Text Block] Vesting [Axis] Vesting [Axis] Series 3 Preferred Stock Series 3 Preferred Stock [Member] Series 3 Preferred Stock Fixed assets Deferred Tax Liabilities, Property, Plant and Equipment Depreciation Deferred Tax Assets, Property, Plant and Equipment Computer Equipment [Member] Computer Equipment [Member] Class of Warrant or Right [Domain] Class of Warrant or Right [Domain] City Area Code City Area Code Prepaid expenses and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Exercisable at end of period (in usd per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Related Party [Axis] Related Party [Axis] Risk-free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Common stock reserved for issuance (in shares) Common Stock, Capital Shares Reserved for Future Issuance Counterparty Name [Axis] Counterparty Name [Axis] Concentration Risk [Table] Concentration Risk [Table] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Others, net Deferred Tax Liabilities, Other Property and Equipment Property, Plant and Equipment, Policy [Policy Text Block] Accrued payroll and benefits Increase (Decrease) in Employee Related Liabilities Rent expense Operating Leases, Rent Expense Furniture and Fixtures [Member] Furniture and Fixtures [Member] Assets Assets [Abstract] Sale Of Stock, Shares Authorized To Be Sold Sale Of Stock, Shares Authorized To Be Sold Sale Of Stock, Shares Authorized To Be Sold Tax credits Deferred Tax Assets, Tax Credit Carryforwards Par value of preferred stock (in usd per share) Preferred Stock, Par or Stated Value Per Share Entity Ex Transition Period Entity Ex Transition Period Rental income from noncancelable sublease Operating Leases, Rent Expense, Sublease Rentals Proceeds from issuance of Series 3 convertible preferred stock Proceeds from Issuance of Convertible Preferred Stock 2022 Finite-Lived Intangible Assets, Amortization Expense, Year Three Promissory note Notes Payable, Fair Value Disclosure Schedule of Finite-Lived Intangible Assets, Future Amortization Expense Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Net Cash Provided by (Used in) Operating Activities [Abstract] Net Cash Provided by (Used in) Operating Activities [Abstract] Accounts payable due to related parties Due to Related Parties Property and Equipment, Impairment Property, Plant and Equipment, Impairment [Policy Text Block] Sale of Products Sale of Products [Member] Sale of Products Schedule of stockholders' equity note, warrants or rights Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block] Others, net Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent Stock options exercised Stock Issued During Period, Value, Stock Options Exercised Net loss per share - basic and diluted Earnings Per Share, Basic and Diluted Intangible assets, net Total Finite-Lived Intangible Assets, Net Minimum number of days before closing Contractual Minimum Number of Days Before Closing Contractual Minimum Number of Days Before Closing Customer [Domain] Customer [Domain] Debt Disclosure [Abstract] Maximum number of shares of common stock issuable (in shares) Debt Instrument, Convertible, Number of Equity Instruments Schedule of maturities of long-term debt Schedule of Maturities of Long-term Debt [Table Text Block] Schedule of inventory Schedule of Inventory, Current [Table Text Block] Convertible Preferred Stockholder Convertible Preferred Stockholder [Member] Convertible Preferred Stockholder Income Statement Location [Domain] Income Statement Location [Domain] Related party transaction expenses Related Party Transaction, Expenses from Transactions with Related Party Statistical Measurement [Axis] Statistical Measurement [Axis] Supplemental disclosures of cash flow information: Supplemental Cash Flow Information [Abstract] Loss on disposal of property and equipment Gain (Loss) on Disposition of Property Plant Equipment The 2015 Plan The 2015 Plan [Member] The 2015 Plan Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] Accounts payable and accrued expenses Accounts Payable and Accrued Liabilities, Current Options outstanding, aggregate intrinsic value Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Changes in operating assets and liabilities: Increase (Decrease) in Other Operating Assets and Liabilities, Net [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Statement of Financial Position [Abstract] Revenue Recognition Revenue from Contract with Customer [Policy Text Block] Shares redeemed (in shares) Shares redeemed (in shares) Stock Repurchased During Period, Shares 2022 Long-term Debt, Maturities, Repayments of Principal in Year Three KKR Phorm Investors L.P. (KKR) KKR Phorm Investors L.P. (KKR) [Member] KKR Phorm Investors L.P. (KKR) Expected volatility, minimum Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate, Minimum Debts Debt Disclosure [Text Block] Options authorized (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized Schedule of Finite-Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] Shares issued in connection with the Reverse Merger Stock Issued During Period, Value, New Issues Related To Merger Stock Issued During Period, Value, New Issues Related To Merger Convertible preferred stock, liquidation rights per share Temporary Equity, Liquidation Preference Per Share Common stock, shares authorized (in shares) Common Stock, Shares Authorized License Maintenance Fee License Maintenance Fee [Member] License Maintenance Fee Accumulated Amortization Finite-Lived Intangible Assets, Accumulated Amortization Customer A Customer A [Member] Customer A Statement of Cash Flows [Abstract] Entity Central Index Key Entity Central Index Key Convertible preferred stock, authorized (in shares) Temporary Equity, Shares Authorized Equity Awards outstanding under The 2020 Plan (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Entity Emerging Growth Company Entity Emerging Growth Company Weighted average grant date fair value Share-Based Compensation Arrangement By Share-Based Payment Award, Fair Value Assumptions, Weighted Average Grant Date Fair Value Share-Based Compensation Arrangement By Share-Based Payment Award, Fair Value Assumptions, Weighted Average Grant Date Fair Value Sale of Stock [Domain] Sale of Stock [Domain] Stock-based compensation Share-based Payment Arrangement, Noncash Expense Proceeds from issuance of revolving credit facility Proceeds from Lines of Credit Others, net Deferred Tax Assets, Other Fujitsu Semiconductor Limited Fujitsu Semiconductor Limited [Member] Fujitsu Semiconductor Limited Minimum percentage of fair market value of common stock Share-Based Compensation Arrangement By Share-based Payment Award, Fair Value Assumptions, Exercise Price, Percent Fair Market Value Share-Based Compensation Arrangement By Share-based Payment Award, Fair Value Assumptions, Exercise Price, Percent Fair Market Value State and Local Jurisdiction State and Local Jurisdiction [Member] Placement agent fees and closing expenses Payments of Stock Issuance Costs Income Taxes Income Tax, Policy [Policy Text Block] Fair value at January 1, Fair value at December 31, Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value Accrued payroll and benefits Employee-related Liabilities, Current Level 2 Fair Value, Inputs, Level 2 [Member] Research and development credit Effective Income Tax Rate Reconciliation, Tax Credit, Research, Percent Income Taxes Income Tax Disclosure [Text Block] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Concentration Risk Type [Axis] Concentration Risk Type [Axis] Deferred Revenue Deferred Revenue [Member] Deferred Revenue Fair Value Measurement Fair Value Measurement, Policy [Policy Text Block] Preferred stock, shares issued (in shares) Preferred Stock, Shares Issued Warrant Warrant [Member] Revenue Revenue from Contract with Customer Benchmark [Member] Research and Development Research and Development Expense, Policy [Policy Text Block] Deferred Tax Assets, Tax Deferred Expense [Abstract] Deferred Tax Assets, Tax Deferred Expense [Abstract] Other assets Other Assets, Noncurrent Depreciation and amortization related to property, plant, and equipment Depreciation And Amortization On Property, Plant, And Equipment Depreciation And Amortization On Property, Plant, And Equipment Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Weighted Average Remaining Contractual Term (in Years) Share-Based Compensation Arrangement By Share-Based Payment Award, Weighted Average Remaining Contractual Term [Abstract] Share-Based Compensation Arrangement By Share-Based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Accounts payable and accrued expenses Increase (Decrease) in Accounts Payable and Accrued Liabilities The 2020 Equity Incentive Plan The 2020 Equity Incentive Plan [Member] The 2020 Equity Incentive Plan Aggregate principal amount of loans outstanding Total Long-term Debt 2023 Finite-Lived Intangible Assets, Amortization Expense, Year Four Development loans, net of current portion Loans Payable, Noncurrent Segment Reporting Segment Reporting, Policy [Policy Text Block] Unsecured subordinated convertible promissory note Convertible Subordinated Debt Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Purchases of property and equipment Payments to Acquire Property, Plant, and Equipment Proceeds from Issuance of debt Proceeds from Issuance of Long-term Debt Foreign Exchange Rate Changes Finite Lived Intangible Assets, Accumulated Change in Foreign Exchange Rate Finite Lived Intangible Assets, Accumulated Change in Foreign Exchange Rate Aizu Fajitsu Semiconductor Wafer Solution Limited Variable Interest Entity, Not Primary Beneficiary [Member] Conversion of stock (in shares) Conversion of Stock, Shares Issued Other Receivable Other Receivable [Member] Other Receivable Commitment to acquire equipment and services from vendors Purchase Commitment, Amount Purchase Commitment, Amount Unfunded commitment to joint venture Other Liabilities, Current Sale of Stock [Axis] Sale of Stock [Axis] Subsequent Event [Table] Subsequent Event [Table] Related Party Services Related Party Services [Member] Related Party Services Estimated weighted average amortization period (in years) Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Accounting Policies [Abstract] Percent of price paid by purchasers of preferred stock Debt Instrument, Qualified Financing, Percentage Of Price Per Share Debt Instrument, Qualified Financing, Percentage Of Price Per Share Additional Paid-in Capital Additional Paid-in Capital [Member] Equipment purchased Purchase Commitment, Equipment Purchase And Reimbursement Purchase Commitment, Equipment Purchase And Reimbursement Net operating loss carryforwards Deferred Tax Assets, Operating Loss Carryforwards Stock-Based Compensation Share-based Payment Arrangement [Policy Text Block] Notes payable Notes Payable Accounts Receivable Accounts Receivable [Member] UNITED STATES UNITED STATES Common stock, forfeited and cancelled (in shares) Common Stock, Forfeited And Cancelled Common Stock, Forfeited And Cancelled Tranche B Loan Tranche B Loan [Member] Tranche B Loan Interest rate per annum Debt Instrument, Interest Rate, Stated Percentage 2021 Long-term Debt, Maturities, Repayments of Principal in Year Two Entity Address, Address Line One Entity Address, Address Line One Property, Plant and Equipment, Gross Property, Plant and Equipment, Gross Future minimum rental payments to be received under sublease Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Gross loss Gross Profit Geographical [Domain] Geographical [Domain] Property and Equipment Property, Plant and Equipment Disclosure [Text Block] Principal payments on promissory notes Repayments of Notes Payable Entity Address, State or Province Entity Address, State or Province Income Statement Location [Axis] Income Statement Location [Axis] Common Stockholder Common Stockholder [Member] Common Stockholder Customer Concentration Risk Customer Concentration Risk [Member] Term of stock options Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period Retirement Benefits [Abstract] Share-based Payment Arrangement, Tranche One Share-based Payment Arrangement, Tranche One [Member] Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Related Party Transaction Related Party Transaction [Line Items] Grant reimbursement Research And Development Expense Reimbursement Research And Development Expense Reimbursement Private placement offering cost Noncash Stock Issuance Costs Noncash Stock Issuance Costs Transphorm Aizu, Inc. Transphorm Ailzu, Inc. [Member] Transphorm Ailzu, Inc. November 2020 Expiration Date 1 [Member] Expiration Date 1 Transphorm Japan, Inc. Transphorm Japan, Inc. [Member] Transphorm Japan, Inc. Income Tax Authority [Axis] Income Tax Authority [Axis] General and administrative General and Administrative Expense Put and call rights term Joint Venture Agreement, Put and Call Rights, Term Joint Venture Agreement, Put and Call Rights, Term Proceeds from Collaborators Proceeds from Collaborators Letter of intent to provide funding Letter Of Intent, Current Year Commitment To Provide Funding Letter Of Intent, Current Year Commitment To Provide Funding Nexperia Nexperia [Member] Nexperia Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Income Tax Authority, Name [Axis] Income Tax Authority, Name [Axis] Developed technology - 150V Developed Technology - 150V [Member] Developed Technology - 150V Effect of exchange rate change Effect Of Exchange Rate On Variable Interest Entity Earnings Effect Of Exchange Rate On Variable Interest Entity Earnings 2020 Operating Leases, Future Minimum Payments, Remainder of Fiscal Year Common stock, shares issued (in shares) Common Stock, Shares, Issued Noncontrolling Common Stockholder Noncontrolling Common Stockholder [Member] Noncontrolling Common Stockholder Common stock, par value (in usd per share) Common Stock, Par or Stated Value Per Share Total operating expenses Costs and Expenses Percentage of cash and cash equivalents in foreign subsidiary Cash and Cash Equivalents, at Carrying Value, Percentage In Foreign Currency Cash and Cash Equivalents, at Carrying Value, Percentage In Foreign Currency Inventory Total Inventory, Net Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Minimum aggregate proceeds of underwritten public offering of stock Temporary Equity, Conversion Basis, Minimum Aggregate Proceeds Of Underwritten Public Offering Of Stock Temporary Equity, Conversion Basis, Minimum Aggregate Proceeds Of Underwritten Public Offering Of Stock Accrued interest on promissory note Interest Expense, Debt Changes in fair value of promissory notes Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Measurement Frequency [Axis] Measurement Frequency [Axis] Long-term assets Assets, Noncurrent Schedule of convertible preferred stock by class Schedule of Stock by Class [Table Text Block] Options available for grant (in shares) Beginning balance, available for grant (in shares) Ending balance, available for grant (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Conversion price per share on convertible note payable (in dollars per share) Debt Instrument, Convertible, Conversion Price Less: accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment February 2025 Expiration Date 2 [Member] Expiration Date 2 Award Type [Domain] Award Type [Domain] Deferred revenue Deferred Revenue Tranche B-1 Loan Tranche B-1 Loan [Member] Tranche B-1 Loan Products sold to related party Revenue from Related Parties Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] JAPAN JAPAN Intangible Assets Goodwill and Intangible Assets, Intangible Assets, Policy [Policy Text Block] Options granted (in shares) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Leasehold improvements Leasehold Improvements [Member] Issuance of common stock, net (in shares) Stock Issued During Period, Shares, New Issues Percentage of vesting in 1st 12 months Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage Tranche C Loan Tranche C Loan [Member] Tranche C Loan Ownership [Domain] Ownership [Domain] Cost of revenue Cost of Sales [Member] License Fee Income License Fee Income [Member] License Fee Income Research and development Research and Development Expense [Member] Schedule of promissory note obligation Schedule of Long-term Debt Instruments [Table Text Block] Effective tax rate Effective Income Tax Rate Reconciliation, Percent Consolidated Entities [Axis] Consolidated Entities [Axis] Total liabilities Liabilities Restatement [Axis] Restatement [Axis] Schedule of Effective Income Tax Rate Reconciliation Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Reclassification of Prior Year Presentation Reclassification, Policy [Policy Text Block] Common stock Common Stock, Value, Issued Foreign income tax rate difference Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent Sales and marketing Selling and Marketing Expense [Member] Estimated time of regulatory approval, minimum Estimated Time Of Regulatory Approval, Minimum Estimated Time Of Regulatory Approval, Minimum Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Research and development Research and Development Expense Vesting [Domain] Vesting [Domain] Investments By Consolidated And Nonconsolidated Entities [Axis] Investments By Consolidated And Nonconsolidated Entities [Axis] Investments By Consolidated And Nonconsolidated Entities Counterparty Name [Domain] Counterparty Name [Domain] Statement of Comprehensive Income [Abstract] Inventory Increase (Decrease) in Inventories Expected volatility, maximum Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate, Maximum Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Tax Year 2018 Tax Year 2018 [Member] Transphorm, Inc. Transphorm, Inc. [Member] Transphorm, Inc. Nexperia Arrangement Collaborative Arrangement Disclosure [Text Block] Aggregate Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] Equity Components [Axis] Equity Components [Axis] Net deferred tax assets Deferred Tax Assets, Net Investment in joint venture Investment in joint venture Payments to Acquire Equity Method Investments Supplemental non-cash financing activity: Additional Cash Flow Elements [Abstract] Total stockholders’ deficit Beginning balance Ending balance Stockholders' Equity Attributable to Parent Operating Loss Carryforwards [Table] Operating Loss Carryforwards [Table] Amortization expense Amortization of Intangible Assets Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Deferred tax asset, net of valuation allowance Deferred Tax Assets, Net of Valuation Allowance Commitment For Services Commitment For Services [Member] Commitment For Services Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Fair Value Measurements Fair Value Disclosures [Text Block] Finite-Lived Intangible Assets [Line Items] Finite-Lived Intangible Assets [Line Items] Shares issued in connection with the Reverse Merger (in shares) Stock Issued During Period, Shares, New Issues Related To Merger Stock Issued During Period, Shares, New Issues Related To Merger Transphorm Epi, Inc. Transphorm Epi, Inc. [Member] Transphorm Epi, Inc. Loan repayment Repayments of Other Debt Depreciation and amortization Depreciation, Depletion and Amortization Conversion of shares in connection with the Reverse Merger Stock Issued During Period, Value, Conversion of Convertible Securities Deferred tax assets, valuation allowance before adjustments Deferred Tax Assets, Valuation Allowance Before Adjustments Deferred Tax Assets, Valuation Allowance Before Adjustments Tax Period [Domain] Tax Period [Domain] Gross Finite-Lived Intangible Assets, Gross Interest expense paid Interest Paid, Excluding Capitalized Interest, Operating Activities Other investors with a small percentage Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Forecast Forecast [Member] Goodwill Goodwill and Intangible Assets, Goodwill, Policy [Policy Text Block] Convertible preferred stock, shares outstanding (in shares) Temporary Equity, Shares Outstanding Expected exercise price under certain conditions Joint Venture Agreement, Call Option, Exercise Price Joint Venture Agreement, Call Option, Exercise Price Number of anti-dilutive shares (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Related Party Transaction [Axis] Related Party Transaction [Axis] Variable Interest Entity, Measure of Activity [Abstract] Variable Interest Entity, Measure of Activity [Abstract] Net cash used in operating activities Net Cash Provided by (Used in) Operating Activities Equity Component [Domain] Equity Component [Domain] Weighted average expected life (in years) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Deferred revenue Increase (Decrease) in Contract with Customer, Liability Investments By Consolidated Entities [Domain] Investments By Consolidated Entities [Domain] Investments By Consolidated Entities 2020 Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months Stock options Share-based Payment Arrangement, Option [Member] Minimum ratio offering price per share of OIP Temporary Equity, Conversion Basis, Offering Price Minimum, Ratio to Original Issue Price Temporary Equity, Conversion Basis, Offering Price Minimum, Ratio to Original Issue Price Convertible preferred stock, price per share (in usd per share) Temporary Equity, Redemption Price Per Share Loss Variable Interest Entity, Measure of Activity, Operating Income or Loss Total deferred tax assets Deferred Tax Assets, Gross Consolidated Entities [Domain] Consolidated Entities [Domain] Goodwill impairment charges Goodwill, Impairment Loss Tranche A Loan Tranche A Loan [Member] Tranche A Loan 2022 Operating Leases, Future Minimum Payments, Due in Three Years Underwritten public offering of common stock, minimum aggregate net proceeds Temporary Equity, Conversion Basis, Minimum Aggregate Proceeds Of Underwritten Public Offering Of Common Stock Temporary Equity, Conversion Basis, Minimum Aggregate Proceeds Of Underwritten Public Offering Of Common Stock Patents Patents [Member] Income Statement [Abstract] Upper limit of estimated enterprise value Debt Instrument, Qualified Financing, Limit of Estimated Enterprise Value, Maximum Debt Instrument, Qualified Financing, Limit of Estimated Enterprise Value, Maximum Investment in Aizu Fujitsu Semiconductor Water Solution Limited ("AFSW") Variable Interest Entity Disclosure [Text Block] Balance Sheet Location [Axis] Balance Sheet Location [Axis]