Leases - Total lease cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 26, 2019
Finance lease costs:
Amortization of finance lease assets	$ 2,851	$ 3,507
Interest on lease liabilities	1,048	1,247
Total finance lease costs	3,899	4,754
Operating lease costs:
Operating lease costs	25,821	24,302
Variable lease cost	724	1,560
Short-term lease cost	321	237
Total operating lease costs	$ 26,866	$ 26,099