Balance sheet components - Expected revenue recognition (Details) $ in Thousands	Mar. 28, 2020 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Deferred revenue expected to be recognized	$ 60,343
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-03-29
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Deferred revenue expected to be recognized	$ 7,503
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligations expected to be satisfied in	6 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-05
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Deferred revenue expected to be recognized	$ 13,727
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligations expected to be satisfied in	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-10-04
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Deferred revenue expected to be recognized	$ 11,881
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligations expected to be satisfied in	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-10-03
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Deferred revenue expected to be recognized	$ 9,953
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligations expected to be satisfied in	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-10-02
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Deferred revenue expected to be recognized	$ 17,279
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligations expected to be satisfied in