Condensed Consolidated Statements of Changes in Stockholders' Equity (unaudited) - USD ($) $ in Millions	Total	Common	Accumulated Deficit	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Treasury
Beginning balance (in shares) at Dec. 31, 2023		68,000,000.0
Beginning balance (in shares) at Dec. 31, 2023						0
Beginning balance at Dec. 31, 2023	$ 660.0	$ 0.1	$ (1,332.7)	$ 1,995.7	$ (3.1)	$ 0.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	64.9			64.9
Net loss	(153.8)		(153.8)
Issuance of common stock under equity incentive plans (in shares)		700,000
Issuance of common stock under equity incentive plans	7.7			7.7
Unrealized gain on available-for-sale securities	7.2				7.2
Ending balance (in shares) at Sep. 30, 2024		68,700,000
Ending balance (in shares) at Sep. 30, 2024						0
Ending balance at Sep. 30, 2024	586.0	$ 0.1	(1,486.5)	2,068.3	4.1	$ 0.0
Beginning balance (in shares) at Jun. 30, 2024		68,600,000
Beginning balance (in shares) at Jun. 30, 2024						0
Beginning balance at Jun. 30, 2024	600.2	$ 0.1	(1,437.3)	2,041.2	(3.8)	$ 0.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	24.7			24.7
Net loss	(49.2)		(49.2)
Issuance of common stock under equity incentive plans (in shares)		100,000
Issuance of common stock under equity incentive plans	2.4			2.4
Unrealized gain on available-for-sale securities	7.9				7.9
Ending balance (in shares) at Sep. 30, 2024		68,700,000
Ending balance (in shares) at Sep. 30, 2024						0
Ending balance at Sep. 30, 2024	$ 586.0	$ 0.1	(1,486.5)	2,068.3	4.1	$ 0.0
Beginning balance (in shares) at Dec. 31, 2024	68,800,000	68,800,000
Beginning balance (in shares) at Dec. 31, 2024	0					0
Beginning balance at Dec. 31, 2024	$ 561.7	$ 0.1	(1,531.6)	2,092.2	1.0	$ 0.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	35.5			35.5
Net loss	(13.4)		(13.4)
Issuance of common stock under equity incentive plans (in shares)		1,200,000
Issuance of common stock under equity incentive plans	$ 0.5			0.5
Issuance of common stock for pre-funded warrants (in shares)		3,400,000
Share repurchases (treasury stock) (in shares)	2,560,030					2,600,000
Share repurchases (treasury stock)	$ (20.3)					$ (20.3)
Unrealized gain on available-for-sale securities	$ 0.4				0.4
Ending balance (in shares) at Sep. 30, 2025	70,800,000	73,400,000
Ending balance (in shares) at Sep. 30, 2025	2,600,000					2,600,000
Ending balance at Sep. 30, 2025	$ 564.4	$ 0.1	(1,545.0)	2,128.2	1.4	$ (20.3)
Beginning balance (in shares) at Jun. 30, 2025		73,200,000
Beginning balance (in shares) at Jun. 30, 2025						0
Beginning balance at Jun. 30, 2025	609.3	$ 0.1	(1,509.9)	2,118.1	1.0	$ 0.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	10.1			10.1
Net loss	$ (35.1)		(35.1)
Issuance of common stock under equity incentive plans (in shares)		200,000
Share repurchases (treasury stock) (in shares)	2,560,030					2,600,000
Share repurchases (treasury stock)	$ (20.3)					$ (20.3)
Unrealized gain on available-for-sale securities	$ 0.4				0.4
Ending balance (in shares) at Sep. 30, 2025	70,800,000	73,400,000
Ending balance (in shares) at Sep. 30, 2025	2,600,000					2,600,000
Ending balance at Sep. 30, 2025	$ 564.4	$ 0.1	$ (1,545.0)	$ 2,128.2	$ 1.4	$ (20.3)