Note 6 - Stock Options and Restricted Stock Awards	3 Months Ended
Mar. 31, 2020
Notes to Financial Statements
Share-based Payment Arrangement [Text Block]	6 – Stock Options and Restricted Stock Awards Valuation and Expense Information The Company accounts for stock-based compensation in accordance with ASC 718-10, “Compensation – Stock Compensation,” which requires the measurement and recognition of compensation expense for all share-based payment awards made to our employees and directors, including employee stock options, restricted stock unit awards, restricted stock awards and employee stock purchases related to the Employee Stock Purchase Plan based on estimated fair values. Stock-based compensation expense, calculated using the Black-Scholes option-pricing model for employee stock options and included in selling, general and administrative expense, was $8.6 million for the three months ended March 31, 2020, and $8.8 million for the three months ended March 31, 2019. As of March 31, 2020, the Company had $11.0 million of unrecognized compensation cost related to non-vested employee stock options to be recognized over a weighted-average period of 2.5 years and $13.4 million of unrecognized compensation cost related to non-vested restricted stock units and restricted stock awards to be recognized over a weighted-average period of 1.6 years.

Note 6 - Stock Options and Restricted Stock Awards

3 Months Ended

Mar. 31, 2020

Share-based Payment Arrangement [Text Block]

6 – Stock Options and Restricted Stock Awards

Valuation and Expense Information

The Company accounts for stock-based compensation in accordance with ASC 718-10, “Compensation – Stock Compensation,” which requires the measurement and recognition of compensation expense for all share-based payment awards made to our employees and directors, including employee stock options, restricted stock unit awards, restricted stock awards and employee stock purchases related to the Employee Stock Purchase Plan based on estimated fair values.

Stock-based compensation expense, calculated using the Black-Scholes option-pricing model for employee stock options and included in selling, general and administrative expense, was $8.6 million for the three months ended March 31, 2020, and $8.8 million for the three months ended March 31, 2019.

As of March 31, 2020, the Company had $11.0 million of unrecognized compensation cost related to non-vested employee stock options to be recognized over a weighted-average period of 2.5 years and $13.4 million of unrecognized compensation cost related to non-vested restricted stock units and restricted stock awards to be recognized over a weighted-average period of 1.6 years.