Note 7 - Earnings Per Share - Shares Used to Calculate Earnings Per Share (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Weighted average number of shares used in computation of basic earnings per share add: (in shares)	51,036	50,709
Additional shares from the assumed exercise of employee stock options (in shares)	490	303
Weighted average number of shares used in computation of diluted earnings per share (in shares)	51,526	51,012