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Goodwill and other intangible assets - Goodwill (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 28, 2019
Dec. 29, 2018
Goodwill and Intangible Assets Disclosure [Abstract]    
Goodwill, Acquired During Period $ 2,050  
Goodwill [Roll Forward]    
Goodwill 118,896 $ 121,440
Acquisition   830
Effect of foreign currency translation (2,214) (3,374)
Goodwill $ 118,732 $ 118,896