Note 1 - Summary of Significant Accounting Policies - Estimated Fair Market Value Assumptions - ESPP (Details) - $ / shares |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Expected volatility | 26.30% | 32.60% | 37.40% |
| Dividend yield | 0.83% | 0.00% | 0.00% |
| Risk-free interest rate | 0.26% | 0.02% | 0.04% |
| Expected life (Year) | 91 days | 91 days | 91 days |
| Fair value (in dollars per share) | $ 5.31 | $ 5.08 | $ 4.69 |