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

Dispositions - Additional Information (Details) - USD ($)		1 Months Ended	3 Months Ended		9 Months Ended
	Nov. 04, 2015	Feb. 28, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2017
Asset Purchase Agreement and Ology Bioservices License Agreement [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Cash payments from Ology Bioservices		$ 4,500,000
Number of shares removed from obligation to issue of common stock		23,008
Contingent upon achieving certain specified future operating objectives		$ 3,000,000
Amount entitled to receive							$ 1,600,000
Milestone payment earned				$ 3,000,000
Amount received from sale of discontinued operation			$ 500,000	$ 300,000	$ 2,500,000	$ 700,000
Biodefense Business [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Sales of business, number of common stock shares eligible to receive	23,008
Royalties receivable percentage on net sales	15.00%
Biodefense Business [Member] \| Maximum [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Cash payments from Ology Bioservices	$ 4,500,000