Note 8 - Stock-based Compensation - Non-vested Restricted Stock Options (Details) - Restricted Stock [Member] |
9 Months Ended |
|---|---|
|
Sep. 30, 2016
$ / shares
shares
| |
| Restricted stock at December 31, 2015 (in shares) | shares | 124,393 |
| Restricted stock at December 31, 2015 (in dollars per share) | $ / shares | $ 68.97 |
| Granted (in shares) | shares | 159,705 |
| Granted (in dollars per share) | $ / shares | $ 59.43 |
| Restrictions lapsed (in shares) | shares | (40,779) |
| Restrictions lapsed (in dollars per share) | $ / shares | $ 67.85 |
| Forfeited (in shares) | shares | (19,645) |
| Forfeited (in dollars per share) | $ / shares | $ 63.99 |
| Restricted stock at September 30, 2016 (in shares) | shares | 223,674 |
| Restricted stock at September 30, 2016 (in dollars per share) | $ / shares | $ 62.80 |