Net loss per share attributable to common stockholders - Computation (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Numerator:
Net loss attributable to common stockholders	$ (208,726)	$ (204,618)	$ (217,863)
Denominator:
Weighted-average shares used in computing net loss per share, basic (in shares)	58,016	56,885	53,885
Weighted-average shares used in computing net loss per share, diluted (in shares)	58,016	56,885	53,885
Net loss per share attributable to common stockholders—basic (in dollars per share)	$ (3.60)	$ (3.60)	$ (4.04)
Net loss per share attributable to common stockholders—diluted (in dollars per share)	$ (3.60)	$ (3.60)	$ (4.04)