Commitments and Contingencies (Details) € in Millions	1 Months Ended		3 Months Ended
	Feb. 28, 2017 EUR (€)	Apr. 30, 2013 ft²	Mar. 31, 2017 USD ($) item	Mar. 31, 2017 GBP (£) ft²	Mar. 31, 2017 USD ($) ft²	Dec. 31, 2016 USD ($)	Feb. 29, 2016 USD ($) ft²	Dec. 31, 2015 USD ($)	Apr. 30, 2014 USD ($)	Dec. 31, 2013 USD ($)
Operating leases
Construction allowance					$ 5,718,000	$ 5,914,000
Minimum rental commitments under the non-cancelable operating lease agreements
2017 (nine months remaining)					5,959,000
2018					7,736,000
2019					7,235,000
2020					7,283,000
2021					7,107,000
Thereafter					30,794,000
Total minimum lease payments					66,114,000
Obligations under capital leases					0
Collaborations and Licenses
Potential milestone payable					161,800,000
Amount reimbursable by a third party					1,200,000
Obligation to make payment to vendor for certain contractual services | £				£ 300,000
Manufacturing Commitments
Collaborations and Licenses
Obligation to make payment to vendor for certain contractual services | €	€ 46.2
Other commitment					8,600,000
Due 2017					6,800,000
Due 2018					$ 1,800,000
Term of agreement	5 years
Noncancelable commitment | €	€ 6.3
830 Winter Street, Waltham, MA
Operating leases
Area of space leased | ft²				110,000	110,000
Number of additional terms for which lease agreement can be extended | item			2
Lease term extension period			5 years
Construction allowance								$ 186,000	$ 1,100,000	$ 746,000
930 Winter Street, Walham, MA
Operating leases
Area of space leased | ft²							10,281
Construction allowance							$ 617,000
333 Providence Hwy, Norwood MA
Operating leases
Lease term extension period			5 years
100 River Ridge Drive, Norwood, MA
Operating leases
Area of space leased | ft²		7,507
Lease term extension period		5 years
Lease term period		5 years 2 months
Facilities rent expense, net of sublease income			$ 169,000