Summary of Significant Accounting Policies - Additional Information (Detail) $ in Millions	12 Months Ended	47 Months Ended
Dec. 31, 2015 USD ($) Segment	Dec. 31, 2015 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Property and equipment, estimated useful lives	3 years
Reportable segment \| Segment	1
Leasehold Improvements \| Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Property and equipment, estimated useful lives	4 years
Leasehold Improvements \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Property and equipment, estimated useful lives	6 years
Merck KGaA
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront and milestone payments received to date \| $	$ 110	$ 110
Evofosfamide \| Collaborative Arrangement Product Agreement \| Merck KGaA
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage share of eligible worldwide development expenses	70.00%

Merck KGaA's percentage share of worldwide development expenses.

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+ References

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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Cash received from collaborators during the current period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3536-108585

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

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