Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Oct. 01, 2017	Sep. 30, 2018	Oct. 01, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 2,780		$ 5,767	$ 9,541	$ 18,678
Effective tax rate	23.30%		21.70%	50.10%	26.70%
Provisional (benefit) amount related to one-time transition tax on mandatory deemed repatriation of foreign earnings	$ (4,000)			$ (4,000)		$ 21,700
Potential exposure for BEAT				800
Additional income tax expense		$ 48,300
Provisional amounts related to remeasurement of certain deferred tax assets and liabilities						$ 26,600
Possible reduction in liabilities for uncertain tax positions	$ 900			$ 900