Commitments and Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2013	May 20, 2016
Commitments And Contingencies Disclosure [Line Items]
Operating lease expiration date	2018-02
Operating lease rent expense	$ 700,000	$ 700,000
License fees payable			$ 100,000
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
CMC ICOS Biologics, Inc.
Commitments And Contingencies Disclosure [Line Items]
Contractual obligation payments	$ 3,300,000			$ 3,800,000