Leases (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Income and expenses, lessee [Line Items]
Finance lease cost, amortization of right-of-use asset	$ 570	$ 339	$ 1,404	$ 1,024
Finance lease cost, interest expense on lease liabilities	45	28	103	91
Total lease cost	7,716	5,676	22,133	16,568
Operating expense [Member]
Income and expenses, lessee [Line Items]
Operating lease cost	2,877	1,845	7,776	4,912
Other lease cost	1,216	855	3,895	2,585
Selling and marketing expense [Member]
Income and expenses, lessee [Line Items]
Operating lease cost	2,322	2,188	7,127	6,513
Other lease cost	284	195	953	811
General and administrative expense [Member]
Income and expenses, lessee [Line Items]
Operating lease cost	389	214	844	617
Other lease cost	$ 13	$ 12	$ 31	$ 15