Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended
	Apr. 30, 2016	Dec. 31, 2017	Dec. 31, 2016
Product Liability Contingency [Line Items]
Operating Leases, Future Minimum Payments Due		$ 177,000
Other Prepaid Expense, Current		1,100,000	$ 400,000
Other Commitment, Due in Next Twelve Months		1,200,000
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		400,000
Manufacturing Development [Member]
Product Liability Contingency [Line Items]
Other Commitment		200,000
Office Space [Member]
Product Liability Contingency [Line Items]
Operating Leases, Future Minimum Payments Due		100,000
Lab Space [Member]
Product Liability Contingency [Line Items]
Operating Lease Monthly Rental Payments	$ 2,500
Licenses Agreement
Product Liability Contingency [Line Items]
Accounts payable and accrued liabilities		$ 100,000