Investment in Aizu Fujitsu Semiconductor Wafer Solution Limited ("AFSW") - Summarized Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Variable Interest Entity [Line Items]
Current assets	$ 18,557		$ 5,357
Other current liabilities	1,546		1,688
Aizu Fajitsu Semiconductor Wafer Solution Limited
Variable Interest Entity [Line Items]
Current assets	1,019		3,733
Long-term assets	5,382		5,101
Other current liabilities	1,640		931
Net deficit	(18,345)		(15,359)
Variable Interest Entity, Measure of Activity [Abstract]
Sales	1,248	$ 3,212
Gross loss	(2,197)	(1,588)
Net loss	(2,895)	$ (2,300)
Aizu Fajitsu Semiconductor Wafer Solution Limited | Fujitsu Semiconductor Limited
Variable Interest Entity [Line Items]
Accounts payable due to related parties	15,842		17,913
Aizu Fajitsu Semiconductor Wafer Solution Limited | Transphorm, Inc.
Variable Interest Entity [Line Items]
Accounts payable due to related parties	$ 7,199		$ 5,349