Income Taxes - Deferred tax assets (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Mar. 31, 2021
Deferred tax assets:
Net operating loss carryforwards	$ 49,715	$ 47,424
Tax credits	6,171	5,444
California capitalized research and development	40	72
Others, net	564	581
Total deferred tax assets	56,490	53,521
Valuation allowance	(56,550)	(53,481)
Deferred tax asset, net of valuation allowance	(60)	40
Deferred tax liabilities:
Fixed assets	60	(40)
Total deferred tax liabilities	60	(40)
Net deferred tax assets	$ 0	$ 0