Stock-based compensation - Restricted Stock Units Activity (Details) - Restricted Stock Units (RSUs) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Jun. 30, 2022 USD ($) $ / shares shares	Sep. 30, 2021 USD ($) $ / shares shares
Number of Shares
Beginning balance (in shares) | shares	698
Granted (in shares) | shares	946
Vested (in shares) | shares	(263)
Forfeited (in shares) | shares	(125)
Ending balance (in shares) | shares	1,256	698
Expected to vest (in shares) | shares	1,256
Weighted average grant date fair value per share
Beginning balance (in usd per share) | $ / shares	$ 73.27
Granted (in usd per share) | $ / shares	72.37
Vested (in usd per share) | $ / shares	72.53
Forfeited (in usd per share) | $ / shares	75.37
Ending balance (in usd per share) | $ / shares	72.54	$ 73.27
Expected to vest (in usd per share) | $ / shares	$ 72.54
Weighted average remaining contractual term (years)
Weighted average remaining contractual term, Outstanding	2 years 10 months 24 days	2 years 8 months 12 days
Weighted average remaining contractual term, Expected to vest	2 years 10 months 24 days
Aggregate Intrinsic Value
Aggregate intrinsic value, Outstanding | $	$ 43,883	$ 74,613
Aggregate intrinsic value, Expected to vest | $	$ 43,883