Stock-based compensation - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Mar. 30, 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	1,214,328
Exercised (in shares) | shares	(4,794,807)
Forfeited (in shares) | shares	(3,198,652)
Ending balance (in shares) | shares	41,725,051	48,504,182
Options exercisable (in shares) | shares	27,505,569
Options vested and expected to vest (in shares) | shares	39,490,352
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	10.95	$ 10.33
Option exercisable - Weighted Average Exercise Price (in USD per share) | $ / shares	9.19
Options vested and expected to vest - Weighted Average Exercise Price (in USD per share) | $ / shares	$ 10.75
Additional Information
Weighted Average Remaining Contractual Term	6 years 6 months	6 years 7 months 6 days
Option exercisable - Weighted Average Remaining Contractual Term	5 years 6 months
Options vested and expected to vest - Weighted Average Remaining Contractual Term	6 years 4 months 24 days
Aggregate Intrinsic Value | $	$ 79,001	$ 276,959
Options exercisable - Weighted Average Intrinsic Value | $	79,001
Options vested and expected to vest - Weighted Average Intrinsic Value | $	$ 79,001