Stock-based compensation - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Jun. 29, 2019 USD ($) $ / shares shares	Sep. 29, 2018 USD ($) $ / shares shares
Number of Options
Beginning balance (in shares) | shares	48,504,182
Granted (in shares) | shares	1,714,328
Exercised (in shares) | shares	(5,869,451)
Forfeited (in shares) | shares	(4,247,115)
Ending balance (in shares) | shares	40,101,944	48,504,182
Options exercisable (in shares) | shares	27,343,825
Options vested and expected to vest (in shares) | shares	38,174,480
Weighted Average Exercise Price
Beginning balance (in USD per share) | $ / shares	$ 10.33
Granted (in USD per share) | $ / shares
Exercised (in USD per share) | $ / shares
Forfeited (in USD per share) | $ / shares
Ending balance (in USD per share) | $ / shares	11.10	$ 10.33
Option exercisable - Weighted Average Exercise Price (in USD per share) | $ / shares	9.62
Options vested and expected to vest - Weighted Average Exercise Price (in USD per share) | $ / shares	$ 10.93
Additional Information
Weighted Average Remaining Contractual Term	6 years 4 months 24 days	6 years 7 months 6 days
Option exercisable - Weighted Average Remaining Contractual Term	5 years 4 months 24 days
Options vested and expected to vest - Weighted Average Remaining Contractual Term	6 years 3 months 18 days
Aggregate Intrinsic Value | $	$ 82,902	$ 276,959
Options exercisable - Weighted Average Intrinsic Value | $	82,475
Options vested and expected to vest - Weighted Average Intrinsic Value | $	$ 82,792