Segment Information - Financial Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Segment Reporting Information [Line Items]
Revenue	$ 41.9	$ 102.4	$ 253.1	$ 204.2
Less:
Total research and development expense	64.7	86.9	224.1	264.9
General and administrative expense	21.0	75.8	72.9	131.3
Income tax expense	0.3	0.6	0.1	1.0
Interest income, net	9.0	14.3	31.0	41.9
Segment net loss	(35.1)	(49.2)	(13.4)	(153.8)
Reportable Segment
Segment Reporting Information [Line Items]
Revenue	41.9	102.4	253.1	204.2
Less:
Non program-specific external expense	12.8	13.7	37.9	43.4
Compensation and related personnel expense (including stock-based compensation)	21.6	35.8	88.6	110.4
Other research and development expense	2.8	3.4	8.4	9.4
Total research and development expense	64.7	86.9	224.1	264.9
General and administrative expense	21.0	75.8	72.9	131.3
Other segment expense, net	0.0	2.6	0.4	2.7
Income tax expense	0.3	0.6	0.1	1.0
Interest income, net	9.0	14.3	31.0	41.9
Segment net loss	(35.1)	(49.2)	(13.4)	(153.8)
Reportable Segment | Vepdegestrant ARV-471
Less:
Program-specific external expense	14.2	19.6	53.4	63.8
Reportable Segment | ARV-102
Less:
Program-specific external expense	5.0	4.5	15.3	7.5
Reportable Segment | ARV-806
Less:
Program-specific external expense	5.1	0.8	7.7	1.1
Reportable Segment | ARV-393
Less:
Program-specific external expense	2.6	1.7	7.7	4.6
Reportable Segment | Bavdegalutamide (ARV-110)
Less:
Program-specific external expense	0.3	2.7	2.3	6.8
Reportable Segment | Luxdegalutamide (ARV-766)
Less:
Program-specific external expense	0.0	4.7	0.0	17.9
Reportable Segment | Other programs
Less:
Program-specific external expense	$ 0.3	$ 0.0	$ 2.8	$ 0.0