For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Data Type:	num:percentItemType
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Summary of Significant Accounting Policies - Segments (Details) - item	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Information
Number of operating segments			1
CytomX
Segment Information
Percentages of revenue recognized	14.00%	1.00%	7.00%	20.00%
Roche
Segment Information
Percentages of revenue recognized	77.00%	77.00%	57.00%	27.00%
Sanofi
Segment Information
Percentages of revenue recognized				47.00%
Takeda
Segment Information
Percentages of revenue recognized	2.00%	13.00%	29.00%	4.00%