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
-Publisher FASB
-Name Accounting Standards Codification
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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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Summary of Significant Accounting Policies - Segments (Details) - item	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Information
Number of operating segments			1
Other customers
Segment Information
Percentages of revenue recognized	0.00%	0.00%	0.00%	0.00%
CytomX
Segment Information
Percentages of revenue recognized		14.00%		7.00%
Roche
Segment Information
Percentages of revenue recognized	99.00%	77.00%	99.00%	57.00%
Takeda
Segment Information
Percentages of revenue recognized		2.00%		29.00%