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License fees payable.

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Operating lease commencement date.

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Operating lease expiration date.

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Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Net rentable area for properties owned.

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Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income.

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Commitments and Contingencies - Additional Information (Detail)	1 Months Ended		12 Months Ended
	Feb. 28, 2018 USD ($)	Nov. 30, 2017 ft²	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2013 USD ($)	Feb. 21, 2018 USD ($)	May 20, 2016 USD ($)
Commitments And Contingencies Disclosure [Line Items]
Operating lease expiration date			2018-02
Operating lease rent expense			$ 800,000	$ 700,000
License fees payable					$ 100,000
AGC Biologics, Inc
Commitments And Contingencies Disclosure [Line Items]
Contractual obligation payments			700,000				$ 3,800,000
AGC Biologics, Inc \| Subsequent Event
Commitments And Contingencies Disclosure [Line Items]
Contractual obligation payments						$ 5,600,000
ISU Abxis \| Maximum
Commitments And Contingencies Disclosure [Line Items]
Potential milestone payments			2,000,000
Pfizer Inc \| Collaboration Agreement \| Maximum
Commitments And Contingencies Disclosure [Line Items]
Obligated to make milestone and royalty payments upon achievement of clinical, regulatory and commercial milestones			$ 17,500,000
Pfizer Inc \| Subsequent Event \| Collaboration Agreement
Commitments And Contingencies Disclosure [Line Items]
Milestone payment	$ 1,000,000
South San Francisco, California \| New Office Lease Agreement
Commitments And Contingencies Disclosure [Line Items]
Leased area \| ft²		8,606
Operating lease term of contract		5 years 2 months
Operating lease commencement date		Feb. 16, 2018