Stock-based compensation - stock option rollforward information (Details) - Common stock $ / shares in Units, shares in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2026 USD ($) $ / shares shares
Number of options outstanding
Beginning balance (in shares) | shares	11.7
Granted (in shares) | shares	6.9
Exercised (in shares) | shares	(0.8)
Forfeited (in shares) | shares	(7.9)
Ending balance (in shares) | shares	9.9
Weighted average exercise price per outstanding option
Beginning balance (in dollars per share) | $ / shares	$ 21.18
Granted (in dollars per share) | $ / shares	10.81
Exercised (in dollars per share) | $ / shares	13.19
Forfeited (in dollars per share) | $ / shares	20.41
Ending balance (in dollars per share) | $ / shares	$ 15.03
Other information about options outstanding
Aggregate intrinsic value | $	$ 23.9
Weighted average remaining term	7 years 3 months 18 days
Information about options expected to vest and exercisable
Options expected to vest, number (in shares) | shares	6.2
Options expected to vest, weighted average exercise price per option (in dollars per share) | $ / shares	$ 11.56
Options expected to vest, aggregate intrinsic value | $	$ 22.9
Options expected to vest, weighted average remaining term	9 years 3 months 18 days
Options exercisable, number (in shares) | shares	3.7
Options exercisable, weighted average exercise price per option (in dollars per share) | $ / shares	$ 20.81
Options exercisable, aggregate intrinsic value | $	$ 1.0
Options exercisable, weighted average remaining term	4 years