Investment in Aizu Fujitsu Semiconductor Wafer Solution Limited ("AFSW") - Summarized Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Variable Interest Entity [Line Items]
Current assets	$ 13,321		$ 13,321		$ 5,357
Other current liabilities	1,548		1,548		1,688
Aizu Fajitsu Semiconductor Wafer Solution Limited
Variable Interest Entity [Line Items]
Current assets	1,827		1,827		3,733
Long-term assets	5,367		5,367		5,101
Other current liabilities	2,830		2,830		931
Net deficit	(22,166)		(22,166)		(15,359)
Variable Interest Entity, Measure of Activity [Abstract]
Sales	538	$ 3,039	1,786	$ 6,251
Gross loss	(3,148)	(1,579)	(5,345)	(3,167)
Net loss	(3,789)	$ (2,245)	(6,684)	$ (4,545)
Aizu Fajitsu Semiconductor Wafer Solution Limited | Fujitsu Semiconductor Limited
Variable Interest Entity [Line Items]
Accounts payable due to related parties	17,421		17,421		17,913
Aizu Fajitsu Semiconductor Wafer Solution Limited | Transphorm, Inc.
Variable Interest Entity [Line Items]
Accounts payable due to related parties	$ 9,109		$ 9,109		$ 5,349