Stock-based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 01, 2023	Jun. 30, 2021	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation cost related to unvested awards not yet recognized			$ 76.5		$ 76.5
Expected weighted-average period compensation cost to be recognized					2 years 9 months 14 days
Weighted average grant date fair value (in dollars per share)					$ 1.69	$ 4.33
2021 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common shares reserved for future issuance (in shares)		26,662,087
Award expiration period		10 years
Proportion of stock outstanding (as a percent)		5.00%
Number of additional shares authorized for issuance (in shares)	12,478,367
Increase in proportion of common shares reserved for future issuance (as a percent)	5.00%
Vesting period		4 years
Future issuance of common shares (in shares)			22,478,430		22,478,430
Stock-based compensation (in shares)			0	0	542,921	283,574
2021 Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award expiration period		10 years
2021 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common shares reserved for future issuance (in shares)		2,470,000
Award expiration period		10 years
Proportion of stock outstanding (as a percent)		1.00%
Number of additional shares authorized for issuance (in shares)	0
Future issuance of common shares (in shares)			3,905,099		3,905,099
Purchase of common stock at discount (as a percent)		15.00%
Employee purchase of shares, proportion of fair value (as a percent)		85.00%
Maximum number of shares to be purchased under ESPP (in shares)		4,940,000
Maximum offering period		27 months
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award expiration period							10 years
Vesting period							4 years
Future issuance of common shares (in shares)							0