Unaudited Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Oct. 01, 2016	Sep. 30, 2017	Oct. 01, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ (3,305)	$ 4,997	$ 3,752	$ 21,521
Other comprehensive income (loss):
Unrealized holding gain (loss) on available-for-sale investments arising during the period, net of income taxes	534	(147)	717	467
Realized (gain) on available-for-sale investments reclassified into income, net of taxes	(387)	(29)	(571)	(53)
Unrealized changes in fair value of interest rate swaps, net of income taxes	55	45	34	(389)
Foreign currency translation adjustments	713	(293)	888	(990)
Total other comprehensive income (loss)	915	(424)	1,068	(965)
Total comprehensive (loss) income	$ (2,390)	$ 4,573	$ 4,820	$ 20,556