Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Apr. 30, 2016	Dec. 31, 2018	Dec. 31, 2017
Product Liability Contingency [Line Items]
Operating Leases, Future Minimum Payments Due		$ 154,000
Other Prepaid Expense, Current		300,000	$ 1,100,000
Other Commitment, Due in Next Twelve Months		1,000,000
Lessee, Operating Lease, Liability, Payments, Due		100,000
Drug Supplier Project Plan [Member]
Product Liability Contingency [Line Items]
Other Commitment		1,600,000
Manufacturer Of Prexigebersen [Member]
Product Liability Contingency [Line Items]
Other Commitment		1,000,000
Manufacture Of Drug Substance [Member]
Product Liability Contingency [Line Items]
Other Commitment		500,000
Manufacturing Development [Member]
Product Liability Contingency [Line Items]
Other Commitment		100,000
Lab Space [Member]
Product Liability Contingency [Line Items]
Operating Lease Monthly Rental Payments	$ 2,500
Extended Lab Space [Member]
Product Liability Contingency [Line Items]
Operating Leases, Future Minimum Payments Due		100,000
Operating Lease Monthly Rental Payments		$ 2,575