Note 8 - Earnings Per Share - Shares Used to Calculate Earnings Per Share (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Weighted average number of shares used in computation of basic earnings per share (in shares)	50,367	49,599	49,942	49,410
Additional shares from the assumed exercise of employee stock options (in shares)	500	690	727	687
Weighted average number of shares used in computation of diluted earnings per share (in shares)	50,867	50,289	50,669	50,097