Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended		9 Months Ended
	Oct. 31, 2019	Jul. 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Apr. 30, 2019
Other Commitments [Line Items]
Research and development			$ 35,692,000	$ 18,508,000	$ 90,378,000	$ 59,544,000
European Patent Office Proceeding [Member]
Other Commitments [Line Items]
Liability related to third party opposition			0		0
University of Pennsylvania [Member] | Maximum [Member]
Other Commitments [Line Items]
Upfront fee, milestone fees							$ 20,500,000
Neurimmune AG [Member]
Other Commitments [Line Items]
Period for sharing of research and development cost		2 years
Percentage of partnership in collaboration		50.00%
Neurimmune AG [Member] | Maximum [Member]
Other Commitments [Line Items]
Research and development			$ 100,000		$ 100,000
Clearside Biomedical Inc. [Member] | Subsequent Event
Other Commitments [Line Items]
Payments against exercise of license option	$ 1,600,000
Clearside Biomedical Inc. [Member] | Maximum [Member] | Subsequent Event
Other Commitments [Line Items]
Upfront fee, milestone fees	$ 136,000,000.0