Note 8 - Stock-based Compensation - Assumptions Used in the Black-Scholes Option Pricing Model (Details) - Employee Stock Option [Member] |
9 Months Ended | |
|---|---|---|
Sep. 30, 2016 |
Sep. 30, 2015 |
|
| Minimum [Member] | ||
| Risk-free interest rate | 1.53% | 1.69% |
| Expected life (years) | 5 years 182 days | |
| Expected volatility | 44.38% | 46.80% |
| Maximum [Member] | ||
| Risk-free interest rate | 1.68% | 1.77% |
| Expected life (years) | 6 years 182 days | |
| Expected volatility | 45.93% | 47.23% |
| Expected life (years) | 6 years 182 days | |
| Expected dividend yield | 0.00% | 0.00% |