Stock Based Compensation (Details)	3 Months Ended	9 Months Ended
Sep. 30, 2020 shares	Sep. 30, 2020 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)	5,057,986	5,057,986
Percentage of outstanding shares	5.00%	5.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		4 years
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)	5,042,525	5,042,525
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock granted (in shares)	816,180	816,180
Equity awards immediately vested	4,000	4,000
Restricted Stock Units (RSUs) \| Period 1
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage vesting		33.33%
Restricted Stock Units (RSUs) \| Period 2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage vesting		33.33%
Restricted Stock Units (RSUs) \| Period 3
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage vesting		33.33%
Restricted Stock Awards (RSA)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock granted (in shares)	123,501	123,501
Equity awards immediately vested	86,450	86,450
Restricted Stock Awards (RSA) \| Period 1
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage vesting	70.00%
Restricted Stock Awards (RSA) \| Period 2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	120 days
The 2020 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)	1,902,922	1,902,922
Equity Awards outstanding under The 2020 Plan (in shares)	816,180	816,180
Number of shares authorized by 2020 plan (in shares)	5,050,000	5,050,000
The 2020 Equity Incentive Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options authorized (in shares)		2,461,923
Annual increase in shares available for issue		5,000,000
Transphorm Technology 2007 Stock Plan and 2015 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized by 2020 plan (in shares)	2,588,077	2,588,077

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