Nature of the business and basis of presentation - Initial public offering (Details) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended
	May 28, 2019 $ / shares shares	Jun. 30, 2019 shares	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($) shares
Share capital reorganization and share split
Offering expenses | $				$ 8.4
Ordinary Shares
Share capital reorganization and share split
Shares issued (in shares)				4,637,666
Conversion of convertible preferred shares to ordinary shares (in shares)				11,647,529
IPO
Share capital reorganization and share split
Shares issued (in shares)	4,333,333
Share price (in dollars per share) | $ / shares	$ 14.00
Proceeds from IPO, net | $			$ 56.4
Underwriting discounts and commissions | $			4.5
Offering expenses | $			$ 4.0
IPO | Ordinary Shares
Share capital reorganization and share split
Conversion of convertible preferred shares to ordinary shares (in shares)	11,647,529
Conversion ratio	0.6997
Over allotment option
Share capital reorganization and share split
Shares issued (in shares)		304,333