Subsequent Events - Additional Information (Detail) - Subsequent Event [Member]	Aug. 07, 2015 USD ($)	Jul. 22, 2015 USD ($) ft²	Jul. 13, 2015 USD ($)
Cambridge, Massachusetts [Member] | July 22, 2015 Amendment [Member]
Subsequent Event [Line Items]
Leased space | ft²		13,843
Additional future minimum lease payments due through expiration		$ 2,200,000
Aggregate leasehold improvement allowance		$ 500,000
Cowen and Company Llc [Member]
Subsequent Event [Line Items]
Net proceeds from issuance of common stock	$ 7,700,000
Maximum [Member] | Cowen and Company Llc [Member] | At the Market Offering [Member]
Subsequent Event [Line Items]
Aggregate sales price of offering			$ 40,000,000