Note 3 - Stock-based Compensation - Stock-based Compensation Expense by Financial Statement Line Item (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2022
Total stock-based compensation expense	$ 1,140	$ 1,440	$ 3,608	$ 3,492
Cost of Sales [Member]
Total stock-based compensation expense	62	89	230	195
Research and Development Expense [Member]
Total stock-based compensation expense	158	214	469	570
Selling, General and Administrative Expenses [Member]
Total stock-based compensation expense	$ 920	$ 1,137	$ 2,909	$ 2,727