Condensed Consolidated Statements of Operations and Comprehensive Loss (unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Income Statement [Abstract]
Revenue	$ 41.9	$ 102.4	$ 253.1	$ 204.2
Operating expenses:
Research and development	64.7	86.9	224.1	264.9
General and administrative	21.0	75.8	72.9	131.3
Total operating expenses	85.7	162.7	297.0	396.2
Loss from operations	(43.8)	(60.3)	(43.9)	(192.0)
Other income
Other expense, net	0.0	(2.6)	(0.4)	(2.7)
Interest income, net	9.0	14.3	31.0	41.9
Total other income	9.0	11.7	30.6	39.2
Net loss before income taxes	(34.8)	(48.6)	(13.3)	(152.8)
Income tax expense	(0.3)	(0.6)	(0.1)	(1.0)
Net loss	$ (35.1)	$ (49.2)	$ (13.4)	$ (153.8)
Loss per common share
Basic (in dollars per share)	$ (0.48)	$ (0.68)	$ (0.18)	$ (2.14)
Diluted (in dollars per share)	$ (0.48)	$ (0.68)	$ (0.18)	$ (2.14)
Weighted average common shares outstanding
Basic (in shares)	73.2	72.1	72.9	71.9
Diluted (in shares)	73.2	72.1	72.9	71.9
Condensed Consolidated Statements of Comprehensive Income (Loss)
Net loss	$ (35.1)	$ (49.2)	$ (13.4)	$ (153.8)
Other comprehensive loss:
Unrealized gain on available-for-sale securities	0.4	7.9	0.4	7.2
Comprehensive loss	$ (34.7)	$ (41.3)	$ (13.0)	$ (146.6)