Stockholders’ Deficit - Equity incentive plans (Narrative) (Details) - USD ($) shares in Millions, $ in Millions	9 Months Ended
Sep. 30, 2025	Dec. 31, 2024
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued and outstanding (in shares)	0.0	0.1
2018 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
Remaining unamortized stock-based compensation	$ 640.5
Award requisite period	2 years 9 months 18 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)	25.8
Shares available for grant (in shares)	131.9

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

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