Condensed Consolidated Statements of Operations and Comprehensive (Loss) Income (unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Income Statement [Abstract]
Revenue	$ 22.4	$ 76.5	$ 211.2	$ 101.8
Operating expenses:
Research and development	68.6	93.7	159.4	178.0
General and administrative	25.3	31.3	51.9	55.6
Total operating expenses	93.9	125.0	211.3	233.6
Loss from operations	(71.5)	(48.5)	(0.1)	(131.8)
Other income
Other expense, net	(0.3)	(0.1)	(0.4)	(0.1)
Interest income, net	10.3	13.6	22.0	27.6
Total other income	10.0	13.5	21.6	27.5
Net (loss) income before income taxes	(61.5)	(35.0)	21.5	(104.3)
Income tax benefit (expense)	0.3	(0.2)	0.2	(0.3)
Net (loss) income	$ (61.2)	$ (35.2)	$ 21.7	$ (104.6)
(Loss) earnings per common share
Basic (in dollars per share)	$ (0.84)	$ (0.49)	$ 0.30	$ (1.46)
Diluted (in dollars per share)	$ (0.84)	$ (0.49)	$ 0.30	$ (1.46)
Weighted average common shares outstanding
Basic (in shares)	73.0	71.9	72.8	71.7
Diluted (in shares)	73.0	71.9	73.0	71.7
Condensed Consolidated Statements of Comprehensive Income (Loss)
Net (loss) income	$ (61.2)	$ (35.2)	$ 21.7	$ (104.6)
Other comprehensive loss:
Unrealized (loss) gain on available-for-sale securities	(0.5)	0.6	0.0	(0.7)
Comprehensive (loss) income	$ (61.7)	$ (34.6)	$ 21.7	$ (105.3)