Revenue Impact of changes in accounting polices (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 28, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 29, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	$ 859,428	$ 842,049	$ 827,324	$ 835,104	$ 853,130	$ 812,576	$ 846,646	$ 875,374	$ 3,363,905	$ 3,387,726	$ 3,662,251
Cost of sales and operating expenses									2,589,085	2,646,374	$ 2,875,680
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									184,835	177,726
Cost of sales and operating expenses									184,835	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									3,548,740	3,565,452
Cost of sales and operating expenses									$ 2,773,920	$ 2,824,100