Restatement of Previously Issued Financial Statements - Income Statement (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Reclassification [Line Items]
Collaborations, milestones, and royalties	$ 17,796,000	$ 59,164,000	$ 57,700,000	$ 123,649,000
Loss from operations	(55,197,000)	(18,270,000)	(165,230,000)	(105,011,000)
Interest expense	(9,026,000)	(7,000)	(27,984,000)	(21,000)
Loss before income tax expense	(47,442,000)		(190,340,000)
Income tax expense	0	0	0	0
Net loss	(47,442,000)	(24,269,000)	(190,340,000)	(106,986,000)
Net loss attributable to non-controlling interest	(1,154,000)	0	(3,275,000)	0
Net loss attributable to Xencor, Inc.	$ (46,288,000)	$ (24,269,000)	$ (187,065,000)	$ (106,986,000)
Basic net loss per common share attributable to Xencor, Inc. (in dollars per share)	$ (0.72)	$ (0.40)	$ (3.00)	$ (1.77)
Diluted net loss per common share attributable to Xencor, Inc. (in dollars per share)	$ (0.72)	$ (0.40)	$ (3.00)	$ (1.77)
As Reported
Reclassification [Line Items]
Collaborations, milestones, and royalties	$ 10,710,000		$ 40,475,000
Loss from operations	(62,283,000)		(182,455,000)
Interest expense	(795,000)		(2,716,000)
Loss before income tax expense	(46,297,000)		(182,297,000)
Income tax expense	0		117,000
Net loss	(46,297,000)		(182,414,000)
Net loss attributable to non-controlling interest	(1,154,000)		(3,275,000)
Net loss attributable to Xencor, Inc.	$ (45,143,000)		$ (179,139,000)
Basic net loss per common share attributable to Xencor, Inc. (in dollars per share)	$ (0.71)		$ (2.87)
Diluted net loss per common share attributable to Xencor, Inc. (in dollars per share)	$ (0.71)		$ (2.87)
Adjustment
Reclassification [Line Items]
Collaborations, milestones, and royalties	$ 7,086,000		$ 17,225,000
Loss from operations	7,086,000		17,225,000
Interest expense	(8,231,000)		(25,268,000)
Loss before income tax expense	(1,145,000)		(8,043,000)
Income tax expense	0		(117,000)
Net loss	(1,145,000)		(7,926,000)
Net loss attributable to non-controlling interest	0		0
Net loss attributable to Xencor, Inc.	$ (1,145,000)		$ (7,926,000)
Basic net loss per common share attributable to Xencor, Inc. (in dollars per share)	$ (0.01)		$ (0.13)
Diluted net loss per common share attributable to Xencor, Inc. (in dollars per share)	$ (0.01)		$ (0.13)