Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended		12 Months Ended
	Jul. 01, 2018	Dec. 31, 2017	Jul. 02, 2017	Jul. 01, 2018	Jul. 02, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 4,368		$ 5,376	$ 6,761	$ 12,911
Effective tax rate	(506.70%)		26.90%	94.90%	29.70%
Additional income tax expense		$ 48,300
Provisional amounts related to remeasurement of certain deferred tax assets and liabilities						$ 26,600
Provisional amount related to one-time transition tax on mandatory deemed repatriation of foreign earnings						$ 21,700
Possible reduction in liabilities for uncertain tax positions	$ 900			$ 900