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Convertible Promissory Notes and Conversion of Convertible Preferred Stock (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013
Conversion of Convertible Promissory Notes and Preferred Stock
Proceeds from the sale of Series A-1 preferred	$ 10,000us-gaap_ProceedsFromIssuanceOfConvertiblePreferredStock

X

- Definition

The cash inflow from issuance of preferred stocks identified as being convertible into another form of financial instrument, typically the entity's common stock.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585

+ Details

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Balance Type:	debit
Period Type:	duration

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- Details

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Namespace Prefix:	xncr_
Data Type:	xbrli:stringItemType
Balance Type:	na
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