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

Capital Stock - ATM Agreements - Additional Information (Details) - USD ($)		1 Months Ended		3 Months Ended
	Dec. 18, 2018	Dec. 31, 2018	Feb. 28, 2017	Mar. 31, 2019	Mar. 31, 2018
Common Stock [Member]
Class Of Warrant Or Right [Line Items]
Sale of shares		285,689	1,200,000		68,000
2018 ATM Agreement [Member]
Class Of Warrant Or Right [Line Items]
Sales commission paid per transaction (in hundredths)	3.00%
Maximum amount of shares can be issued	$ 30,000,000
2018 ATM Agreement [Member] \| Common Stock [Member]
Class Of Warrant Or Right [Line Items]
Sale of shares				0