Income Taxes - Deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Mar. 31, 2022
Deferred tax assets:
Net operating loss carryforwards	$ 53,496	$ 49,715
Tax credits	6,898	6,171
California capitalized research and development	1	40
Research and development	1,708	0
Others, net	679	564
Total deferred tax assets	62,782	56,490
Valuation allowance	(62,933)	(56,550)
Deferred tax asset, net of valuation allowance	(151)	(60)
Deferred tax liabilities:
Fixed assets	151	60
Total deferred tax liabilities	151	60
Net deferred tax assets	$ 0	$ 0