Commitments and Contingencies - Additional Information (Detail)				12 Months Ended
	Nov. 11, 2015 USD ($) ft²	Apr. 02, 2015	Feb. 13, 2015	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Other Commitments [Line Items]
Operating lease agreement expiration date				Jan. 31, 2018
Lease incentive obligation				$ 586,000
Future minimum lease payments in 2016				1,274,000
Future minimum lease payments in 2017				1,162,000
Future minimum lease payments in 2018				643,000
Future minimum lease payments in 2019				478,000
Future minimum lease payments in 2020				80,000
Indemnification Agreement [Member]
Other Commitments [Line Items]
Indemnification obligations accrued				$ 0	$ 0
BMR Sidney Research Campus LLC [Member]
Other Commitments [Line Items]
Non-cancelable property lease, description				On November 11, 2015, the Company entered into a non-cancelable property lease with BMR-Sidney Research Campus LLC (“BMR”) for 83,396 square feet of office, laboratory and pilot manufacturing space at 200 Sidney Street, Cambridge, Massachusetts. The lease term is expected to commence in March 2016 and end in November 2023. The Company has the option to extend the lease twice, each for a five-year period. The Company intends to move its corporate headquarters to this location in mid-
Square feet of property subject to non-cancelable lease | ft²	83,396
Lease commencement period	2016-03
Lease expiration period	2023-11
Cost of tenant improvements	$ 12,509,000
Lease incentive obligation				$ 586,000
Future minimum lease payments in 2016				911,000
Future minimum lease payments in 2017				5,528,000
Future minimum lease payments in 2018				5,694,000
Future minimum lease payments in 2019				5,864,000
Future minimum lease payments in 2020				6,040,000
Future minimum lease payments Thereafter				17,752,000
Office Space [Member]
Other Commitments [Line Items]
Operating lease agreement expiration date			May 31, 2016
Office and Laboratory Space [Member]
Other Commitments [Line Items]
Operating lease agreement expiration date		Apr. 30, 2020
Rental expense related to office and laboratory space				$ 1,246,000	$ 543,000	$ 152,000