Note 2 - Acquisitions - Business Acquisition Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Net sales	$ 434,526	$ 368,813
Income before income taxes	81,924	11,021
Net income	$ 63,933	$ 17,462
Net income per share — basic (in dollars per share)	$ 2.57	$ 0.70
Net income per share — diluted (in dollars per share)	$ 2.53	$ 0.69