Note 1 - Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2017

Notes Tables

Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]

	Three Months Ended						Nine Months Ended
	September 30,			September 24,			September 30,			September 24,
	2017			2016			2017			2016
Cost of sales	$	123		$	101		$	327		$	309
Research and development		278			327			856			955
Selling, general and administrative		1,459			1,330			4,153			4,027
Total share-based compensation		1,860			1,758			5,336			5,291
Income tax benefit		(107	)		(76	)		(429	)		(189	)
Total share-based compensation, net	$	1,753		$	1,682		$	4,907		$	5,102

Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]

	Three Months Ended				Nine Months Ended
	September 30,		September 24,		September 30,		September 24,
	2017		2016		2017		2016
Weighted average common shares		28,155		26,761		27,614		26,596
Effect of dilutive securities		950		606		1,026		786
		29,105		27,367		28,640		27,382

Schedules of Concentration of Risk, by Risk Factor [Table Text Block]

	Three Months Ended						Nine Months Ended
	September 30,			September 24,			September 30,			September 24,
	2017			2016			2017			2016
Customers individually accounting for more than 10% of net sales		two			three			two			two
Percentage of net sales		26.5	%		37.4	%		28.5	%		30.5	%