XOMA Corporation Quarterly report pursuant to Section 13 or 15(d)

Capital Stock - ATM Agreements (Details) - USD ($) $ in Millions				26 Months Ended	57 Months Ended
	Aug. 05, 2021	Mar. 10, 2021	Dec. 18, 2018	Sep. 30, 2023	Sep. 30, 2023
2018 Common Stock ATM Agreement \| Common Stock
Sale of stock
Maximum amount of shares to be issued		$ 50.0	$ 30.0
Shares issued (in shares)					0
2018 Common Stock ATM Agreement \| Common Stock \| Maximum
Sale of stock
Sales commission paid per transaction (as a percent)			3.00%
2021 ATM Agreement \| Series B Depositary Shares
Sale of stock
Maximum amount of shares to be issued	$ 50.0
Shares issued (in shares)				0
2021 ATM Agreement \| Series B Depositary Shares \| Maximum
Sale of stock
Sales commission paid per transaction, preferred stock (as a percent)	3.00%