Investment in Aizu Fujitsu Semiconductor Wafer Solution Limited ("AFSW") - Summarized Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2021
Variable Interest Entity [Line Items]
Current assets	$ 9,793		$ 14,294
Other current liabilities	1,339		1,866
Aizu Fajitsu Semiconductor Wafer Solution Limited
Variable Interest Entity [Line Items]
Current assets	1,693		932
Long-term assets	5,395		5,330
Other current liabilities	2,495		2,200
Net deficit	(34,526)		(31,471)
Variable Interest Entity, Measure of Activity [Abstract]
Sales	1,430	$ 538
Gross loss	(2,399)	(3,148)
Net loss	(3,041)	$ (3,789)
Fujitsu Semiconductor Limited | Aizu Fajitsu Semiconductor Wafer Solution Limited
Variable Interest Entity [Line Items]
Accounts payable due to related parties	24,299		22,354
Transphorm, Inc. | Aizu Fajitsu Semiconductor Wafer Solution Limited
Variable Interest Entity [Line Items]
Accounts payable due to related parties	$ 14,820		$ 13,179