Segment information Total net revenues by geographic region (Details) - USD ($) $ in Thousands	3 Months Ended
	Apr. 01, 2018	Apr. 02, 2017
Segment Reporting Information [Line Items]
Net revenues	$ 587,230	$ 487,881
United States
Segment Reporting Information [Line Items]
Net revenues	344,357	286,314
Europe
Segment Reporting Information [Line Items]
Net revenues	171,320	141,022
Asia
Segment Reporting Information [Line Items]
Net revenues	49,555	43,004
All Other
Segment Reporting Information [Line Items]
Net revenues	$ 21,998	$ 17,541