Net income (loss) per share attributable to common stockholders - Computation of Basic and Diluted Earnings per Share (Details) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
	Aug. 06, 2018 shares	Jun. 29, 2019 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) $ / shares shares	Jun. 29, 2019 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) $ / shares shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common shares issued in conversion of outstanding shares of redeemable convertible preferred stock (shares)	32,482,590
Number of shares of common stock issued for each share of redeemable convertible preferred stock	1
Numerator:
Net income (loss) | $		$ (14,009)	$ (26,988)	$ 24,834	$ (13,884)
Denominator:
Weighted-average shares of common stock - basic (in shares)		105,522,313	60,074,763	102,667,316	59,484,761
Weighted-average shares of common stock - diluted (in shares)		105,522,313	60,074,763	112,542,998	59,484,761
Net income (loss) attributable to common stockholders:
Net income (loss) per share attributable to common stockholders - basic (in USD per share) | $ / shares		$ (0.13)	$ (0.45)	$ 0.24	$ (0.23)
Net income (loss) per share attributable to common stockholders - diluted (in USD per share) | $ / shares		$ (0.13)	$ (0.45)	$ 0.22	$ (0.23)
Stock Options
Denominator:
Effect of potentially dilutive stock options and RSUs (in shares)		0	0	9,115,070	0
Restricted Stock Units
Denominator:
Effect of potentially dilutive stock options and RSUs (in shares)		0	0	760,612	0