Note 9 - Stock-Based Compensation (Details) - Summary of Option Activity (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Summary of Option Activity [Abstract]
Number of Shares	437,248	398,172	416,125	433,785
Weighted Average Exercise Price	$ 55.81	$ 38.75	$ 29.87	$ 22.77
Weighted Average Remaining Contractual Term	4 years 328 days	4 years 146 days	3 years 255 days	3 years 328 days
Aggregate Intrinsice Value	$ 9,445	$ 20,505	$ 9,529	$ 11,516
Exercisable at March 31,
Number of Shares Exercisable	163,210	140,825	158,320
Weighted Average Exercise Price, Exercisable	$ 33.35	$ 26.70	$ 21.00
Weighted Average Remaining Contractual Term, Exercisable	3 years 219 days	3 years 6 months	3 years
Aggregate Intrinsice Value, Exercisable	$ 6,341	$ 8,949	$ 5,031
Number of Shares Granted	147,720	128,124	116,080
Weighted Average Exercise Price, Granted	$ 88.62	$ 55.33	$ 49.97
Weighted Average Remaining Contractual Term, Granted	7 years	6 years 146 days	5 years 328 days
Number of Shares Forfeited	(26,466)	(27,782)	(40,375)
Weighted Average Exercise Price, Forfeited	$ 64.62	$ 52.50	$ 32.87
Number of Shares Expired		(410)	(40)
Weighted Average Exercise Price, Expired		$ 52.50	$ 18.98
Number of Shares Exercised	(82,178)	(117,885)	(93,325)
Weighted Average Exercise Price, Exercised	$ 28.87	$ 22.17	$ 20.56

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Weighted average remaining contractual term for option awards granted during the reporting period, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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-Publisher FASB

-Name Accounting Standards Codification

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of share options (or share units) exercised during the current period.

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