Share-based compensation - Restricted Stock Units Activity (Details) - RSUs - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 28, 2019	Sep. 29, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding, beginning balance (in shares)	0
Granted (in shares)	7,915,980
Exercised (in shares)	(829,270)
Forfeited (in shares)	(369,924)
Expired (in shares)	0
Outstanding, ending balance (in shares)	6,716,786
Units expected to vest (in shares)	5,207,691
Outstanding (in usd per share)	$ 11.4	$ 0.0
Aggregate Intrinsic Value	$ 90,744	$ 0
Vested and expected to vest - Weighted Average Exercise Price (in dollars per share)	$ 11.4
Vested and expected to vest - Weighted Average Intrinsic Value	$ 70,356