Note 7 - Earnings Per Share - Shares Used to Calculate Earnings Per Share (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Weighted average number of shares used in computation of basic earnings per share add: (in shares)	51,043	50,800	51,040	50,757
Additional shares from the assumed exercise of employee stock options (in shares)	319	294	408	301
Weighted average number of shares used in computation of diluted earnings per share (in shares)	51,362	51,094	51,448	51,058