Note 2 - Acquisitions - Business Acquisition Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Net sales	$ 396,897	$ 893,709	$ 765,710
Income before income taxes	40,312	134,227	51,546
Net income	$ 37,442	$ 106,247	$ 55,043
Net income per share — basic (in dollars per share)	$ 1.50	$ 4.26	$ 2.21
Net income per share — diluted (in dollars per share)	$ 1.48	$ 4.22	$ 2.18