Note 10 - Accounts Payable and Accrued Expenses - Product Warranty Activity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Balance at beginning of period	$ 2,168	$ 1,606	$ 2,015	$ 1,545
Change in accruals for warranties during the period	148	71	384	156
Settlements during the period	(207)	(36)	(290)	(60)
Balance at end of period	$ 2,109	$ 1,641	$ 2,109	$ 1,641