Leases (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019
Income and expenses, lessee [Line Items]
Finance lease cost, amortization of right-of-use asset	$ 483	$ 340	$ 834	$ 685
Finance lease cost, interest expense on lease liabilities	35	29	58	63
Total lease cost	7,030	5,640	14,417	10,892
Operating expense [Member]
Income and expenses, lessee [Line Items]
Operating lease cost	2,660	1,629	4,899	3,067
Other lease cost	912	1,011	2,679	1,730
Selling and marketing expense [Member]
Income and expenses, lessee [Line Items]
Operating lease cost	2,412	2,158	4,805	4,325
Other lease cost	298	270	669	616
General and administrative expense [Member]
Income and expenses, lessee [Line Items]
Operating lease cost	221	202	455	403
Other lease cost	$ 9	$ 1	$ 18	$ 3