Collaboration Agreement - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration and license agreement, nature and purpose	Under this agreement, the Company and ThromboGenics are collaborating to identify protein or peptide therapeutics that directly modulate any of a specified set of targets in a novel pathway in retinal disease.
Collaboration and license agreement, date	May 28, 2013
Collaboration and license arrangement, rights and obligations	The Company has granted ThromboGenics an exclusive, sublicenseable, royalty-bearing license under the Company's rights in these patent rights and know-how, as well as under any other patent rights and know-how that the Company controls during the research term that are necessary for ThromboGenics to perform its obligations to research, develop, manufacture and commercialize collaboration products.
Upfront payment received	$ 1,750,000
Milestone payments receivable	25,000,000
Collaboration revenue	244,000	568,000
Milestone or royalty payments received	0
Upon the Achievement of Specified Preclinical and Clinical Development Milestone Events [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	10,000,000
Upon the Achievement of Specified Regulatory Milestone Events [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	$ 15,000,000