Note 4 - Employee Benefit Plans - Allocated Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jul. 01, 2016	Jun. 30, 2017	Jul. 01, 2016
Allocated share-based compensation expense	$ 628	$ 545	$ 1,105	$ 1,251
Selling, General and Administrative Expenses [Member]
Allocated share-based compensation expense	542	453	984	619
Research and Development Expense [Member]
Allocated share-based compensation expense	86	92	121	163
Other Operating Income (Expense) [Member]
Allocated share-based compensation expense				469
Employee Stock Option [Member]
Allocated share-based compensation expense	239	185	410	248
Restricted Stock Units (RSUs) [Member]
Allocated share-based compensation expense	$ 389	$ 360	$ 695	$ 1,003