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

Dispositions - Additional Information (Details) - USD ($)		1 Months Ended	3 Months Ended
	Nov. 04, 2015	Feb. 28, 2017	Mar. 31, 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			$ 1,000,000		$ 200,000
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