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Note 10 - Stock-based Compensation - Summary of Unvested Options (Details) - $ / shares	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Unvested, Shares (in shares)	373,766	358,263	274,038
Granted, Numbers of Shares (in shares)	96,330	134,955	184,030
Options forfeited, Shares (in shares)	(72,166)	(35,015)	(16,334)
Options vested, Shares (in shares)	(83,408)	(84,437)	(83,471)
Unvested, Shares (in shares)	314,522	373,766	358,263
Unvested, Weighted-average grant-date fair value (in dollars per share)	$ 22.49	$ 19.46	$ 18.42
Options granted, Weighted-average grant-date fair value (in dollars per share)	39.06	31.27	18.78
Options forfeited, Weighted-average grant-date fair value (in dollars per share)	28.43	22.64	19.07
Options vested, Weighted-average grant-date fair value (in dollars per share)	21.84	16.96	14.65
Unvested, Weighted-average grant-date fair value (in dollars per share)	$ 29.01	$ 22.49	$ 19.46

X

- Definition

Gross number of share options (or share units) granted during the period.

+ References

No definition available.

+ Details

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X

- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

Number of non-vested options outstanding.

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- Definition

Number of non-vested options forfeited.

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- Definition

Weighted average grant-date fair value of non-vested options forfeited.

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Weighted average grant-date fair value of non-vested options outstanding.

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