Business overview and basis of presentation (Details) $ / shares in Units, $ in Thousands			9 Months Ended
	Aug. 06, 2018 USD ($) $ / shares shares	Jul. 19, 2018	Jun. 29, 2019 USD ($) country	Jun. 30, 2018 USD ($)
Class of Stock [Line Items]
Number of countries where products are distributed | country			50
Underwriting discounts and commissions | $			$ 585	$ 2,154
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
Stock split, conversion ratio		2
IPO
Class of Stock [Line Items]
Shares sold in IPO (shares)	6,388,888
Public offering price (in USD per share) | $ / shares	$ 15.00
Net proceeds from IPO | $	$ 90,600
Underwriting discounts and commissions | $	5,300
Offering costs | $	$ 4,600
Over-Allotment Option
Class of Stock [Line Items]
Shares sold in IPO (shares)	833,333
Initial Public Offering - Shares From Existing Shareholders
Class of Stock [Line Items]
Shares sold in IPO (shares)	9,583,333
Over-Allotment Option - Shares From Existing Shareholders
Class of Stock [Line Items]
Shares sold in IPO (shares)	1,250,000