Stockholders’ Deficit - Equity incentive plans (Narrative) (Details) - USD ($) shares in Millions, $ in Millions	9 Months Ended
Sep. 30, 2024	Dec. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued and outstanding (in shares)	0.2	0.2
2018 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
Remaining unamortized stock-based compensation	$ 781.9
Award requisite period	2 years 8 months 12 days
2018 Plan \| Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
Vesting period	4 years
Equity Incentive Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued and outstanding (in shares)	34.2
Shares available for grant (in shares)	116.6

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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