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Summary of Significant Accounting Policies - Summary of Collaborators that Represent More Than 10% of Accounts Receivable (Details) - Customer Concentration Risk - Accounts receivable	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
F. Hoffmann-La Roche Ltd and Hoffmann-La Roche Inc. (Roche)
Concentration Risk [Line Items]
Percentage of significant accounts receivable	73.00%
Les Laboratoires Servier and Institut de Recherches Servier (Servier)
Concentration Risk [Line Items]
Percentage of significant accounts receivable	12.00%	31.00%
Janssen Biotech, Inc. (Janssen)
Concentration Risk [Line Items]
Percentage of significant accounts receivable		40.00%
U.S. Government
Concentration Risk [Line Items]
Percentage of significant accounts receivable		19.00%

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13531-108611

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6404-108592

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
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-Section 50
-Paragraph 21
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