Customers that Represent Greater than Ten Percent of Net Revenues from Research Collaborators (Detail) (Revenue from Rights Concentration Risk)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Roche/Arrowhead
Concentration Risk [Line Items]
Concentration risk percentage	56.00%	68.00%	56.00%
Takeda
Concentration Risk [Line Items]
Concentration risk percentage	33.00%	27.00%	22.00%

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/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

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-Section 50

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

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-Section 50

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-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13531-108611

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