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Summary of Significant Accounting Policies - Additional Information (Detail)	Sep. 30, 2017
Casebia Therapeutics LLP [Member]
Summary Of Significant Accounting Policies [Line Items]
Equity method interest, ownership percentage	50.00%

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- Definition

Summary of significant accounting policies.

+ References

No definition available.

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- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

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