Leases - Components of lease expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 29, 2019	Jun. 29, 2019
Operating lease costs
Fixed	$ 30,976	$ 63,119
Short-term	5,129	9,477
Variable	11,441	18,919
Sub-leases	(192)	(409)
Operating lease costs	47,354	91,106
Finance lease costs
Amortization of leased assets	392	824
Interest on lease liabilities	58	89
Finance lease costs	450	913
Net lease costs	47,804	92,019
Cost of sales
Operating lease costs
Fixed	8,169	15,857
Short-term	1,552	2,991
Variable	2,093	4,371
Sub-leases	(41)	(125)
Operating lease costs	11,773	23,094
Finance lease costs
Amortization of leased assets	0	0
Interest on lease liabilities	0	0
Finance lease costs	0	0
Net lease costs	11,773	23,094
Selling, general and administrative expenses
Operating lease costs
Fixed	22,807	47,262
Short-term	3,577	6,486
Variable	9,348	14,548
Sub-leases	(151)	(284)
Operating lease costs	35,581	68,012
Finance lease costs
Amortization of leased assets	392	824
Interest on lease liabilities	58	89
Finance lease costs	450	913
Net lease costs	$ 36,031	$ 68,925