Collaboration and Licensing Agreements (Details)				1 Months Ended					3 Months Ended			9 Months Ended
	Nov. 12, 2021 USD ($) shares	Oct. 01, 2021 USD ($) $ / shares	Mar. 08, 2019	Dec. 31, 2021 USD ($) item	Nov. 30, 2020 USD ($) item	Mar. 31, 2020 item	Feb. 28, 2019	Jan. 31, 2013 Program	Sep. 30, 2022 USD ($) agreement	Sep. 30, 2021 USD ($) agreement	Sep. 30, 2019 item	Sep. 30, 2022 USD ($) agreement	Sep. 30, 2021 USD ($) agreement	Mar. 31, 2022 USD ($)
Collaboration research and licensing agreements
Receivable				$ 66,384,000					$ 44,876,000			$ 44,876,000
Revenue recorded									27,299,000	$ 19,683,000		142,969,000	$ 121,096,000
Other income									(1,000)	(593,000)		(244,000)	(610,000)
Impairment on equity securities									0	600,000		138,000	563,000
Net gains recognized on sale of equity securities													18,301,000
Unrealized gain (loss) recognized on equity securities									5,299,000	1,506,000		(4,676,000)	39,206,000
Net gains recognized on equity securities									5,299,000	1,506,000		(4,676,000)	57,507,000
Accounts receivable				$ 66,384,000					44,876,000			44,876,000
Deferred revenue									35,200,000	13,000,000.0		35,200,000	13,000,000.0
Royalties
Collaboration research and licensing agreements
Revenue recorded									27,200,000	13,400,000		135,900,000	27,400,000
Milestone
Collaboration research and licensing agreements
Revenue recorded												5,000,000.0	14,000,000.0
Research collaboration
Collaboration research and licensing agreements
Revenue recorded									100,000	6,300,000		2,100,000	79,700,000
Alexion Pharmaceuticals, Inc.
Collaboration research and licensing agreements
Revenue recorded									7,300,000	5,800,000		20,200,000	16,400,000
Astellas
Collaboration research and licensing agreements
Revenue recorded												5,000,000.0
Genentech
Collaboration research and licensing agreements
Revenue recorded													2,500,000
Genentech | Collaboration and License Agreement
Collaboration research and licensing agreements
Revenue recognized													2,500,000
MorphoSys
Collaboration research and licensing agreements
Revenue recorded									2,100,000	1,300,000		5,600,000	16,400,000
MorphoSys | Collaboration and License Agreement | Royalties
Collaboration research and licensing agreements
Revenue recognized										1,300,000
Novartis
Collaboration research and licensing agreements
Revenue recorded													41,100,000
Novartis | Collaboration and License Agreement
Collaboration research and licensing agreements
Revenue recognized													41,100,000
Vir
Collaboration research and licensing agreements
Revenue recorded									17,800,000	6,300,000		110,100,000	7,700,000
Option and license agreement | Alexion Pharmaceuticals, Inc.
Collaboration research and licensing agreements
Receivable									12,500,000			12,500,000
Accounts receivable									12,500,000			12,500,000
Deferred revenue									0			0
Number of different target programs | Program								1
Option and license agreement | Alexion Pharmaceuticals, Inc. | Royalties
Collaboration research and licensing agreements
Revenue recognized									7,300,000	5,800,000		20,200,000	16,400,000
Research and License Agreement | Amgen, Inc.
Collaboration research and licensing agreements
Revenue recognized									0	0		0	0
Deferred revenue									0			0
Research and License Agreement | Astellas
Collaboration research and licensing agreements
Revenue recognized									0	0		5,000,000.0	0
Deferred revenue									0			0
Research and License Agreement | Astellas | Milestone
Collaboration research and licensing agreements
Contract asset														$ 5,000,000.0
Collaboration and License Agreement | Genentech
Collaboration research and licensing agreements
Initial cost-sharing percentage			45.00%
Research license term							2 years
Revenue recognized									0	0		0
Collaboration and License Agreement | Genentech | XmAb24306
Collaboration research and licensing agreements
Cost sharing receivable (payable)									(3,200,000)			(3,200,000)
Collaboration and License Agreement | Genentech | Research service
Collaboration research and licensing agreements
Deferred revenue									0			0
Collaboration and License Agreement | Janssen Biotech, Inc
Collaboration research and licensing agreements
Revenue recognized									$ 100,000	$ 6,300,000		$ 2,100,000	$ 37,000,000.0
Number of collaboration and license agreements | agreement									2	2		2	2
Collaboration and License Agreement | MorphoSys
Collaboration research and licensing agreements
Deferred revenue									$ 0			$ 0
Collaboration and License Agreement | MorphoSys | Royalties
Collaboration research and licensing agreements
Receivable									2,000,000.0			2,000,000.0
Revenue recognized									2,100,000			5,600,000	$ 16,400,000
Accounts receivable									2,000,000.0			2,000,000.0
Collaboration and License Agreement | Novartis
Collaboration research and licensing agreements
Revenue recognized									0	$ 0		0
Deferred revenue									0			0
Collaboration and License Agreement | Novartis | Development
Collaboration research and licensing agreements
Cost sharing receivable (payable)									300,000			300,000
Technology License Agreement | Astria/Catabasis
Collaboration research and licensing agreements
Unrealized gain (loss) recognized on equity securities									3,900,000	(2,400,000)		2,300,000	6,700,000
Deferred revenue									0			0
Technology License Agreement | Viridian
Collaboration research and licensing agreements
Number of antibodies | item				3
Revenue recognized									0	0		0	0
Unrealized gain (loss) recognized on equity securities									6,400,000	(600,000)		500,000	0
Deferred revenue									0			0
License Agreement | INmune
Collaboration research and licensing agreements
Net gains recognized on sale of equity securities													18,300,000
Unrealized gain (loss) recognized on equity securities									(5,000,000.0)	4,500,000		(7,500,000)	32,500,000
License Agreement | Zenas Bio Pharma Limited
Collaboration research and licensing agreements
Revenue recognized									0	0		0	0
Purchase amount of share options or equity in noncash transaction					$ 16,100,000
Impairment on equity securities									0	0		0	0
Deferred revenue									0			0
Percentage of equity of private company					15.00%
Number of drug candidates | item					3
Patent License Agreement | Vir
Collaboration research and licensing agreements
Deferred revenue									0			0
Number of different target programs | item						2					2
Patent License Agreement | Vir | Royalties
Collaboration research and licensing agreements
Receivable									17,800,000			17,800,000
Revenue recognized									17,800,000	$ 6,300,000		110,100,000
Accounts receivable									17,800,000			17,800,000
Patent License Agreement | Vir | Milestone
Collaboration research and licensing agreements
Revenue recognized													$ 7,700,000
Second Collaboration And License Agreement | Janssen Biotech, Inc
Collaboration research and licensing agreements
Share development percentage		80.00%
Nonrefundable upfront payment		$ 100,000,000.0
Potential milestone payment		$ 1,187,500,000
Research license term		2 years
Deferred revenue									35,200,000			35,200,000
Cost sharing receivable (payable)									$ 3,700,000			$ 3,700,000
Percentage of responsibility for development costs		20.00%
Second Collaboration And License Agreement | Johnson & Johnson Innovation, JJDC, Inc. | Common Stock
Collaboration research and licensing agreements
Total equity shares | shares	748,062
Proceeds from sale of common stock	$ 28,900,000	$ 25,000,000.0
Term of weighted average price of stock		30 days
Volume-weighted average per share price | $ / shares		$ 33.4197
Second Technology License Agreement | Viridian
Collaboration research and licensing agreements
Research license term				1 year
Development-based | Second Collaboration And License Agreement | Janssen Biotech, Inc
Collaboration research and licensing agreements
Potential milestone payment		$ 289,400,000
Regulatory-based | Second Collaboration And License Agreement | Janssen Biotech, Inc
Collaboration research and licensing agreements
Potential milestone payment		378,100,000
Sales-based | Second Collaboration And License Agreement | Janssen Biotech, Inc
Collaboration research and licensing agreements
Potential milestone payment		$ 520,000,000.0