Note 1 - Business and Significant Accounting Policies - Shares Used to Calculate Earnings Per Share (Details) - shares shares in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Weighted average number of shares used in computation of basic earnings per share (in shares)	49,647	49,599	49,456	49,173	49,074	49,023	48,881	47,244	49,469	48,562	45,508
Additional shares from the assumed exercise of employee stock options (in shares)									671	625	351
Weighted average number of shares used in computation of diluted earnings per share (in shares)	50,293	50,289	50,137	49,782	49,668	51,113	50,600	48,079	50,140	49,187	45,859