Net Loss Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Numerator:
Net loss attributable to Xencor, Inc.	$ (46,288)	$ (24,269)	$ (187,065)	$ (106,986)
Denominator:
Weighted-average common shares outstanding used in computing basic net loss (in shares)	64,022,547	60,621,534	62,310,045	60,387,163
Weighted-average common shares outstanding used in computing diluted net loss (in shares)	64,022,547	60,621,534	62,310,045	60,387,163
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)