Leases - Minimum Future Lease Obligations (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 23, 2020	Dec. 25, 2019	Dec. 27, 2018
Lessee, Lease, Description [Line Items]
Finance Lease, Liability, Payments, Remainder of Fiscal Year	$ 16	$ 54
Operating Leases, Future Minimum Payments Due, Remainder of Fiscal Year	7,611	26,808
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals, Remainder Of Fiscal Year	693	2,754
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals, Next Twelve Months	2,887	2,887
Finance Lease, Liability, Payments Due Year One	66	54
Finance Lease, Liability, Payments, Due Year Two	57	45
Lessee, Operating Lease, Liability, to be Paid, Year One	28,901	25,978
Operating Leases, Future Minimum Payments, Due in Two Years	26,112	24,871
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals, within Two Years	3,284	3,284
Finance Lease, Liability, Payments, Due Year Three	11	0
Operating Leases, Future Minimum Payments, Due in Three Years	23,763	22,309
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals, within Three Years	3,318	3,318
Finance Lease, Liability, Payments, Due Year Four	11	0
Operating Leases, Future Minimum Payments, Due in Four Years	21,469	19,751
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals, within Four Years	3,203	3,203
Thereafter	6	0
Thereafter	142,716	139,454
Thereafter	27,265	27,265
Total	167	153
Total	250,572	259,171
Total	40,650	42,711
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(47,972)	(45,273)
Present value of lease obligations	144	117
Finance Lease, Liability, Undiscounted Excess Amount	(23)	(36)
Less: current maturities	(50)	(34)
Obligations under finance leases, net of current portion	94	83
Finance Lease, Liability, Current	(50)	(34)
Present value of lease obligations	202,600	213,898	$ 222,300
Obligations under operating leases, net of current portion	182,753	197,492
Less: current maturities	(19,847)	(16,406)
Finance Lease, Liability, Noncurrent	$ 94	$ 83
Minimum
Lessee, Lease, Description [Line Items]
Imputed interest rate	2.33%
Maximum
Lessee, Lease, Description [Line Items]
Imputed interest rate	11.10%