Geographic and Group Information (Long-Lived Assets Attributable To Geographic Area) (Details) - USD ($) $ in Thousands	Sep. 25, 2020	Dec. 27, 2019
Revenues from External Customers and Long-Lived Assets [Line Items]
Total long-lived assets	$ 113,389	$ 115,108
North America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total long-lived assets	91,745	91,309
International (Primarily European Countries) [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total long-lived assets	$ 21,644	$ 23,799