Note 11 - Employee Benefit Plan (Details Textual) - USD ($)	12 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Deferred Compensation Arrangement with Individual, Requisite Service Period (Year)		1 year
Defined Contribution Plan With Individual Age (Year)		21 years
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount	$ 245,000	$ 211,000	$ 192,000

Minimum period the individual is required to perform services to be fully vested under the deferred compensation arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 710
-SubTopic 10
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6409961&loc=d3e20487-108367

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration