Lease Commitments (Narrative) (Details) - USD ($) $ in Thousands	Dec. 26, 2020	Dec. 28, 2019	Dec. 29, 2018
Operating Leased Assets [Line Items]
Operating lease right-to-use	$ 199,901	$ 210,196
Operating lease liability	$ 208,229
Percentage of facilities under operating lease	51.00%
Maximum [Member]
Operating Leased Assets [Line Items]
Lease renewal term	20 years
Minimum [Member]
Operating Leased Assets [Line Items]
Lease renewal term	5 years
Accounting Standards Update 2016-02 [Member]
Operating Leased Assets [Line Items]
Operating lease right-to-use			$ 202,000
Operating lease liability			$ 211,000