Note 2 - Net Income Per Share - Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Net income	$ 12,607	$ 13,539	$ 31,403	$ 29,506
Shares used in basic Net income per share (in shares)	135,598	132,997	134,903	132,065
Dilutive effect of stock options, RSUs, ESPP shares, and equity awards with a market condition or performance condition (in shares)	5,926	5,897	5,860	5,614
Shares used in diluted Net income per share (in shares)	141,524	138,894	140,763	137,679
Basic (in dollars per share)	$ 0.09	$ 0.10	$ 0.23	$ 0.22
Diluted (in dollars per share)	$ 0.09	$ 0.10	$ 0.22	$ 0.21
Stock options, RSUs, ESPP shares, and equity awards with a market condition or performance condition excluded as they are antidilutive (in shares)	370	909	514	328