Net Loss Per Share Attributable to Common Stockholders - Computation of the Company’s Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Numerator:
Net loss attributable to common stockholders	$ (77,670)	$ (208,726)	$ (204,618)
Denominator:
Weighted-average shares used in computing net loss per share, basic (in shares)	59,808,000	58,016,000	56,885,000
Weighted-average shares used in computing net loss per share, diluted (in shares)	59,808,000	58,016,000	56,885,000
Net loss per share attributable to common stockholders—basic (in dollars per share)	$ (1.30)	$ (3.60)	$ (3.60)
Net loss per share attributable to common stockholders—diluted (in dollars per share)	$ (1.30)	$ (3.60)	$ (3.60)