Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jul. 01, 2018	Jun. 30, 2019	Jul. 01, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 48,749	$ 56,196	$ 81,853	$ 93,413
Available-for-sale investments:
Net unrealized gain (loss), net of tax of $239 and $8 in the three-month periods and net of tax of $507 and ($106) in the six-month periods, respectively	2,311	490	4,562	(702)
Reclassification of net realized (gain) loss into current operations	(382)	(247)	(422)	(269)
Net change related to available-for-sale investments	1,929	243	4,140	(971)
Foreign currency translation adjustments:
Foreign currency translation adjustments	(663)	(7,253)	(445)	(3,197)
Other comprehensive income (loss), net of tax	1,266	(7,010)	3,695	(4,168)
Total comprehensive income	$ 50,015	$ 49,186	$ 85,548	$ 89,245