Investment in Joint Venture - Summarized financial information (Details) - USD ($) $ in Thousands	3 Months Ended	4 Months Ended	8 Months Ended	12 Months Ended
	Mar. 31, 2021	Jul. 31, 2021	Mar. 31, 2022	Mar. 31, 2022	Dec. 31, 2020
Variable Interest Entity [Line Items]
Current assets	$ 14,294		$ 44,794	$ 44,794
Other current liabilities	1,866		0	0
Variable Interest Entity, Measure of Activity [Abstract]
Gross loss	637			11,520	$ 4,689
Aizu Fajitsu Semiconductor Wafer Solution Limited
Variable Interest Entity [Line Items]
Current assets	932		4,259	4,259
Long-term assets	5,330		3,690	3,690
Other current liabilities	2,200		3,799	3,799
Net surplus (deficit)	(31,471)		4,151	4,151
Variable Interest Entity, Measure of Activity [Abstract]
Sales	842	$ 2,176	6,933		2,976
Gross loss	(2,425)	(3,191)	(6,168)		(11,411)
Net loss	(2,995)	$ (4,260)	(7,707)		$ (13,952)
Fujitsu Semiconductor Limited | Aizu Fajitsu Semiconductor Wafer Solution Limited
Variable Interest Entity [Line Items]
Due to controlling owner	22,354
Transphorm, Inc. | Aizu Fajitsu Semiconductor Wafer Solution Limited
Variable Interest Entity [Line Items]
Due to Transphorm	$ 13,179		0	0
GaNovation | Aizu Fajitsu Semiconductor Wafer Solution Limited
Variable Interest Entity [Line Items]
Due to controlling owner			$ (1)	$ (1)