Note 10 - Stock-based Compensation - Summary of Unvested Options (Details) - $ / shares |
12 Months Ended | ||
|---|---|---|---|
Mar. 31, 2017 |
Mar. 31, 2016 |
Mar. 31, 2015 |
|
| Unvested, Shares (in shares) | 358,263 | 274,038 | 257,347 |
| Unvested, Weighted-average grant-date fair value (in dollars per share) | $ 19.46 | $ 18.42 | $ 11.86 |
| Granted, Numbers of Shares (in shares) | 134,955 | 184,030 | 147,720 |
| Options granted, Weighted-average grant-date fair value (in dollars per share) | $ 31.27 | $ 18.78 | $ 24.49 |
| Options forfeited, Shares (in shares) | (35,015) | (16,334) | (26,466) |
| Options forfeited, Weighted-average grant-date fair value (in dollars per share) | $ 22.64 | $ 19.07 | $ 17.29 |
| Options vested, Shares (in shares) | (84,437) | (83,471) | (104,563) |
| Options vested, Weighted-average grant-date fair value (in dollars per share) | $ 16.96 | $ 14.65 | $ 10.36 |
| Unvested, Shares (in shares) | 373,766 | 358,263 | 274,038 |
| Unvested, Weighted-average grant-date fair value (in dollars per share) | $ 22.49 | $ 19.46 | $ 18.42 |