Collaboration and Licensing Agreements - Narrative (Details)			1 Months Ended					3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 22, 2023 USD ($)	Oct. 01, 2021	Sep. 30, 2024 USD ($)	Jul. 31, 2024 USD ($)	Oct. 31, 2021 USD ($)	Feb. 28, 2019 USD ($)	Jan. 31, 2013 program	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Dec. 31, 2019 target	Dec. 31, 2023 USD ($)
Collaboration research and licensing agreements
Receivable			$ 25,872,000					$ 25,872,000		$ 25,872,000			$ 23,739,000
Collaborations, milestones, and royalties								17,796,000	$ 59,164,000	57,700,000	$ 123,649,000
Impairment on equity securities								0	0	20,430,000	0
Deferred revenue			0					0	9,200,000	0	9,200,000
Royalties
Collaboration research and licensing agreements
Collaborations, milestones, and royalties								0	14,500,000	100,000	41,500,000
Milestone
Collaboration research and licensing agreements
Collaborations, milestones, and royalties								0	46,000,000.0	500,000	61,000,000.0
Alexion
Collaboration research and licensing agreements
Collaborations, milestones, and royalties								15,700,000	31,800,000	42,100,000	53,400,000
Gilead
Collaboration research and licensing agreements
Collaborations, milestones, and royalties								0	6,000,000.0	0	6,000,000
Omeros
Collaboration research and licensing agreements
Collaborations, milestones, and royalties								0	5,000,000.0	0	5,000,000.0
Mabgeek
Collaboration research and licensing agreements
Collaborations, milestones, and royalties								0	0	1,500,000	0
Vir
Collaboration research and licensing agreements
Collaborations, milestones, and royalties								0	0	100,000	1,500,000
Zenas
Collaboration research and licensing agreements
Collaborations, milestones, and royalties								0	0	0	10,000,000.0
Zenas | Preferred Stock
Collaboration research and licensing agreements
Equity shares estimated fair value			0					0		0			64,210,000
Third Party Licensee
Collaboration research and licensing agreements
Collaborations, milestones, and royalties								0	0	7,000,000.0	0
Option and License agreement | Alexion
Collaboration research and licensing agreements
Number of different target programs | program							1
Receivable			15,700,000					15,700,000		15,700,000
Deferred revenue			0					0		0
Option and License agreement | Alexion | Royalties
Collaboration research and licensing agreements
Revenue recognized								15,700,000	11,800,000	42,100,000	33,400,000
Collaboration and License Agreement | Genentech
Collaboration research and licensing agreements
Revenue recognized								0	0	0	0
Initial cost-sharing percentage						45.00%
Royalty milestones						$ 600,000,000
Collaboration and License Agreement | Genentech | Development-based
Collaboration research and licensing agreements
Royalty milestones						115,000,000
Collaboration and License Agreement | Genentech | Regulatory-based
Collaboration research and licensing agreements
Royalty milestones						185,000,000
Collaboration and License Agreement | Genentech | Sales-based
Collaboration research and licensing agreements
Royalty milestones						$ 300,000,000
Collaboration and License Agreement | Genentech | XmAb24306
Collaboration research and licensing agreements
Collaborative arrangement receivable (payable) related to cost sharing development activities			(7,600,000)					(7,600,000)		(7,600,000)
Collaboration and License Agreement | Genentech | Research service
Collaboration research and licensing agreements
Deferred revenue			0					0		0
Collaboration and License Agreement | Janssen
Collaboration research and licensing agreements
Revenue recognized								0	7,500,000	0	7,500,000
Deferred revenue			0					0		0
Collaboration and License Agreement | MorphoSys/Incyte
Collaboration research and licensing agreements
Deferred revenue			0					0		0
Collaboration and License Agreement | MorphoSys/Incyte | Royalties
Collaboration research and licensing agreements
Revenue recognized								2,100,000	2,700,000	6,500,000	6,600,000
Receivable			2,100,000					2,100,000		2,100,000
Second Collaboration And License Agreement | Janssen
Collaboration research and licensing agreements
Revenue recognized								0	6,200,000	0	33,600,000
Receivable			2,300,000					2,300,000		2,300,000
Deferred revenue			0					0		0
Research license term		2 years
Second Collaboration And License Agreement | Janssen | Maximum
Collaboration research and licensing agreements
Percentage of responsibility for development costs		20.00%
Second Collaboration And License Agreement | Janssen | Minimum
Collaboration research and licensing agreements
Share development percentage		80.00%
Technology License Agreement | Mabgeek
Collaboration research and licensing agreements
Deferred revenue			0					0		0
Collaborations, milestones, and royalties								0		1,500,000
Collaborative arrangement nonrefundable upfront fees	$ 1,500,000
Royalty milestones	$ 11,900,000
Technology License Agreement | Vega
Collaboration research and licensing agreements
Revenue recognized					$ 500,000
Collaborations, milestones, and royalties								0	0	500,000	0
Technology License Agreement | Gale
Collaboration research and licensing agreements
Transaction price			7,500,000					7,500,000		7,500,000
Service agreement charges								2,700,000		10,700,000
Payments for repurchase of preferred stock and preference stock			3,000,000.0	$ 3,000,000.0				6,000,000.0
License | Zenas
Collaboration research and licensing agreements
Revenue recognized								0	0	0	10,000,000.0
Deferred revenue									$ 0		0
License | Zenas | Milestone | Preferred Stock
Collaboration research and licensing agreements
Equity shares estimated fair value													$ 10,000,000.0
Patent License Agreement | Vir
Collaboration research and licensing agreements
Number of different target programs | target												2
Receivable			0					0		0
Deferred revenue			0					0		0
Patent License Agreement | Vir | Royalties
Collaboration research and licensing agreements
Revenue recognized										100,000	$ 1,500,000
Patent License Agreement | Third Party Licensee
Collaboration research and licensing agreements
Receivable			0					0		0
Deferred revenue			$ 0					0		0
Collaborations, milestones, and royalties								$ 0		$ 7,000,000.0