Note 3 - Stock-based Compensation - Stock-based Compensation Expense By Financial Statement Line Item (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Total stock-based compensation expense	$ 397	$ 825	$ 646	$ 1,610
Cost of Sales [Member]
Total stock-based compensation expense	21	50	24	90
Research and Development Expense [Member]
Total stock-based compensation expense	92	70	103	121
Selling, General and Administrative Expenses [Member]
Total stock-based compensation expense	$ 283	$ 705	$ 519	$ 1,399

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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