Note 8 - Earnings Per Share - Shares Used to Calculate Earnings Per Share (Details) - shares shares in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Weighted average number of shares used in computation of basic earnings per share (in shares)	50,623	49,771	50,618	49,726
Additional shares from the assumed exercise of employee stock options (in shares)	335	853	383	833
Weighted average number of shares used in computation of diluted earnings per share (in shares)	50,958	50,624	51,001	50,559

Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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