Revenue Impact of changes in accounting polices (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 29, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2016	Oct. 01, 2016	Jul. 02, 2016	Apr. 02, 2016	Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	$ 853,130	$ 812,576	$ 846,646	$ 875,374	$ 952,549	$ 936,262	$ 894,930	$ 878,510	$ 3,387,726	$ 3,662,251	$ 3,391,928
Cost of sales and operating expenses									2,647,083	$ 2,875,443	$ 2,635,333
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales									177,726
Cost of sales and operating expenses									177,726
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales									3,565,452
Cost of sales and operating expenses									$ 2,824,809