Restructuring, acquisition and integration-related costs - Restructuring and Related Costs by Type of Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Apr. 02, 2016	Apr. 04, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring, acquisition and integration-related costs	$ 5,253	$ 6,657
Accelerated depreciation included in restructuring costs		4,360
Cost of Sales [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	5,026	9,844
Acquisition integration-related costs	822	132
Restructuring, acquisition and integration-related costs	5,848	9,976
Selling, General and Administrative Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring costs	227	1,173
Acquisition integration-related costs	967	1,380
Restructuring, acquisition and integration-related costs	$ 1,194	$ 2,553