XOMA Corporation Annual report pursuant to Section 13 and 15(d)

Capital Stock - ATM Agreements - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Feb. 28, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class Of Warrant Or Right [Line Items]
Proceeds from issuance of common stock		$ 10,160,000	$ 57,000	$ 171,000
Common Stock [Member]
Class Of Warrant Or Right [Line Items]
Sale of shares	1,200,000	1,849,000	13,000
2015 ATM Agreement [Member]
Class Of Warrant Or Right [Line Items]
Sales commission paid per transaction (in hundredths)		3.00%
Proceeds from issuance of common stock		$ 600,000	$ 56,000
Offering costs offset against proceeds upon sale of common stock		$ 200,000	$ 56,000
2015 ATM Agreement [Member] \| Common Stock [Member]
Class Of Warrant Or Right [Line Items]
Sale of shares		110,252	10,365	0