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Segment and Geographic Information - Schedule of Customer Concentration by Collaboration Partners (Detail) - Customer Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Percentage of Revenue [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk, percentage	42.00%
Percentage of Revenue [Member] | Astellas-Related party [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk, percentage	21.00%	48.00%	47.00%
Percentage of Revenue [Member] | AstraZeneca [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk, percentage	37.00%	52.00%	53.00%
Percentage of Accounts Receivable [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk, percentage	64.00%
Percentage of Accounts Receivable [Member] | Astellas-Related party [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk, percentage	10.00%	17.00%
Percentage of Accounts Receivable [Member] | AstraZeneca [Member]
Entity Wide Revenue Major Customer [Line Items]
Concentration risk, percentage	26.00%	81.00%

X

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Section 50
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-Name Accounting Standards Codification
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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