Balance sheet components - Expected recognition of deferred revenue (Details) $ in Thousands	Sep. 28, 2019 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Revenue expected to be recognized	$ 56,449
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-09-29
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Revenue expected to be recognized	$ 13,654
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-04
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Revenue expected to be recognized	$ 12,143
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, period	2 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-03
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Revenue expected to be recognized	$ 10,297
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, period	3 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-10-02
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Revenue expected to be recognized	$ 8,369
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, period	4 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-10-01
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Revenue expected to be recognized	$ 11,986
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, period