Leases - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Lessee Lease Description [Line Items]
Operating lease, right-of-use asset	$ 1.0
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PrepaidExpenseAndOtherAssetsCurrent
Operating lease, liability	$ 1.6
Operating Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrent
One Kendall Square in Cambridge, Massachusetts [Member]
Lessee Lease Description [Line Items]
Operating lease expiration month and year	2019-06