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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Weighted average number of shares used in computation of basic earnings per share (in shares)	49,771	49,456	49,726	49,314
Additional shares from the assumed exercise of employee stock options (in shares)	853	681	833	663
Weighted average number of shares used in computation of diluted earnings per share (in shares)	50,624	50,137	50,559	49,977