Note 4 - Equipment and Leasehold Improvements - Components of Equipment and Leasehold Improvements (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Mar. 31, 2025
Equipment and leasehold improvements, gross	$ 37,664	$ 37,529
Less accumulated depreciation and amortization	(29,560)	(28,885)
Construction-in-progress	249	283
Equipment and leasehold improvements, net	8,353	8,927
Equipment [Member]
Equipment and leasehold improvements, gross	22,107	21,972
Leasehold Improvements [Member]
Equipment and leasehold improvements, gross	15,138	15,138
Furniture and Fixtures [Member]
Equipment and leasehold improvements, gross	$ 419	$ 419

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount of structure or a modification to a structure under construction. Includes recently completed structures or modifications to structures that have not been placed into service.

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