License Agreements - Additional Information (Details)	1 Months Ended		3 Months Ended	9 Months Ended
	Nov. 30, 2017 USD ($)	Feb. 01, 2016	Sep. 30, 2018 USD ($) Milestone	Sep. 30, 2018 USD ($) Milestone	Dec. 31, 2017 USD ($)
License Agreements [Line Items]
Revenue			$ 411,000	$ 411,000
Duke University
License Agreements [Line Items]
Sublicensable agreement term		20 years
Sale of licensed products or services				0
Fees payment				300,000
Nonroyalty payment received				1,000,000
Duke University | License
License Agreements [Line Items]
Revenue				1,000,000
Maximum | Achievement Of Clinical Development And Regulatory Milestones | Duke University
License Agreements [Line Items]
Potential milestones payment				2,200,000
Maximum | Commercial Milestones | Duke University
License Agreements [Line Items]
Potential milestones payment				400,000
Minimum | Duke University
License Agreements [Line Items]
Aggregate royalties payment				$ 200,000
MedImmune Limited
License Agreements [Line Items]
License agreement upfront payment	$ 100,000
Number of milestones met | Milestone			0	0
Reimbursement of costs incurred to product storage costs					$ 500,000
MedImmune Limited | Maximum | Achievement Of Clinical Development And Regulatory Milestones
License Agreements [Line Items]
Potential milestones payment	18,000,000
MedImmune Limited | Maximum | Commercial Milestones
License Agreements [Line Items]
Potential milestones payment	$ 50,000,000