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://www.xbrl.org/2003/role/disclosureRef
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Summary of Significant Accounting Policies - Segments (Details) - segment	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Information
Number of operating segments	1
Other customers
Segment Information
Percentages of revenue recognized	0.00%	0.00%	0.00%
CytomX
Segment Information
Percentages of revenue recognized		13.00%	8.00%
Roche
Segment Information
Percentages of revenue recognized	53.00%	64.00%	60.00%
Takeda
Segment Information
Percentages of revenue recognized	1.00%		23.00%
Jazz
Segment Information
Percentages of revenue recognized	46.00%	18.00%