Note 10 - Stock Based Compensation - Compensation Expense (Details) - Stock Option Plan [Member] - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Share-based Payment Arrangement, Expense	$ 464	$ 153
Research and Development Expense [Member]
Share-based Payment Arrangement, Expense	158	50
General and Administrative Expense [Member]
Share-based Payment Arrangement, Expense	282	103
Selling and Marketing Expense [Member]
Share-based Payment Arrangement, Expense	$ 24	$ 0