Note 8 - Earnings Per Share - Shares Used to Calculate Earnings Per Share (Details) - shares shares in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Weighted average number of shares used in computation of basic earnings per share (in shares)	50,709	50,614
Additional shares from the assumed exercise of employee stock options (in shares)	303	437
Weighted average number of shares used in computation of diluted earnings per share (in shares)	51,012	51,051

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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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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