Revenue Impact of changes in accounting policies (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	$ 812,576	$ 936,262	$ 2,534,596	$ 2,709,702
Cost of sales and operating expenses	648,101	$ 742,511	1,979,201	$ 2,129,721
Adjustments | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	39,763		131,399
Cost of sales and operating expenses	39,763		131,399
Balances without adoption of Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	852,339		2,665,995
Cost of sales and operating expenses	$ 687,864		$ 2,110,600