Goodwill and other intangible assets - Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 28, 2019	Dec. 29, 2018
Finite-Lived Intangible Assets, Net [Abstract]
Cost	$ 71,231	$ 71,053
Accumulated Amortization	58,879	46,780
Net	12,352	24,273
Completed technology
Finite-Lived Intangible Assets, Net [Abstract]
Cost	28,100	26,900
Accumulated Amortization	24,605	21,607
Net	3,495	5,293
Tradename
Finite-Lived Intangible Assets, Net [Abstract]
Cost	100	100
Accumulated Amortization	100	100
Net	0	0
Customer relationships
Finite-Lived Intangible Assets, Net [Abstract]
Cost	11,095	11,291
Accumulated Amortization	2,302	1,365
Net	8,793	9,926
Reacquired distribution rights
Finite-Lived Intangible Assets, Net [Abstract]
Cost	31,680	32,499
Accumulated Amortization	31,680	23,598
Net	0	8,901
Non-competition agreements
Finite-Lived Intangible Assets, Net [Abstract]
Cost	256	263
Accumulated Amortization	192	110
Net	$ 64	$ 153