Income Tax Rate reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Income Tax [Abstract]
Expected federal income tax expense at statutory rate	$ 12,492	$ 17,553	$ 40,892	$ 49,983
State income taxes before valuation allowance, net of federal tax effect	378	(119)	1,076	90
Effect of foreign source income	(4,771)	(7,372)	(7,117)	(18,017)
Tax contingencies	21	1,577	834	2,112
Valuation allowance	1,002	808	1,455	2,045
U.S. federal research credit	673	(3,026)	(901)	(4,174)
Equity compensation	147	(67)	(5,645)	(2,859)
Global Intangible Low Tax Income	1,102	0	3,051	0
Other items, net	383	(106)	1,110	221
Income tax expense	$ 11,427	$ 9,248	$ 34,755	$ 29,401