Balance sheet components - Accrued expenses (Details) - USD ($) $ in Thousands	Mar. 28, 2020	Sep. 28, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accrued advertising and marketing	$ 13,320	$ 25,662
Accrued taxes	2,468	4,388
Accrued inventory	4,657	6,494
Accrued manufacturing, logistics and product development	13,215	14,783
Accrued general and administrative expenses	6,693	12,455
Other accrued payables	2,688	6,074
Total accrued expenses	$ 43,041	$ 69,856