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Collaboration Agreements - Summary of Revenue Recognized Under the Collaboration Agreements - Additional Information 4 (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
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Sep. 30, 2018 | Jun. 30, 2018 | Sep. 30, 2018
Japan [Member] |  |  |
Revenue Recognition, Multiple-deliverable Arrangements [Line Items] |  |  |
Remainder of transaction price, variable consideration from estimated future co-development billing | $ 2.1 |  |
Japan [Member] | Astellas Agreement [Member] |  |  |
Revenue Recognition, Multiple-deliverable Arrangements [Line Items] |  |  |
Changes in revenue due to prior period adjustment |  | $ 14.9 |
Europe [Member] |  |  |
Revenue Recognition, Multiple-deliverable Arrangements [Line Items] |  |  |
Remainder of transaction price, variable consideration from estimated future co-development billing |  |  | $ 19.4
Europe [Member] | Astellas Agreement [Member] |  |  |
Revenue Recognition, Multiple-deliverable Arrangements [Line Items] |  |  |
Changes in revenue due to prior period adjustment |  |  | (0.1)
U.S./RoW and China [Member] |  |  |
Revenue Recognition, Multiple-deliverable Arrangements [Line Items] |  |  |
Remainder of transaction price, variable consideration from estimated future co-development billing |  |  | 223.7
U.S./RoW and China [Member] | AstraZeneca Agreements [Member] |  |  |
Revenue Recognition, Multiple-deliverable Arrangements [Line Items] |  |  |
Changes in revenue due to prior period adjustment |  |  | $ (0.1)

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- Definition Amount of revenue recognized arising from contract liability from change in timeframe for performance obligation to be satisfied. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130551-203045 + Details
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- Details
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- Details
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- Details
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- Details
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- Details
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