Leases - Components of lease expense (Details) $ in Thousands	3 Months Ended
	Mar. 30, 2019 USD ($)
Operating lease costs
Fixed	$ 32,143
Short-term	4,348
Variable	7,478
Sub-leases	(217)
Operating lease costs	43,752
Finance lease costs
Amortization of leased assets	432
Interest on lease liabilities	31
Finance lease costs	463
Net lease costs	44,215
Cost of sales
Operating lease costs
Fixed	7,688
Short-term	1,439
Variable	2,278
Sub-leases	(84)
Operating lease costs	11,321
Finance lease costs
Amortization of leased assets	0
Interest on lease liabilities	0
Finance lease costs	0
Net lease costs	11,321
Selling, general and administrative expenses
Operating lease costs
Fixed	24,455
Short-term	2,909
Variable	5,200
Sub-leases	(133)
Operating lease costs	32,431
Finance lease costs
Amortization of leased assets	432
Interest on lease liabilities	31
Finance lease costs	463
Net lease costs	$ 32,894