Commitments and Contingencies (Details) € in Millions	6 Months Ended	12 Months Ended
	Dec. 31, 2016 USD ($) ft²	Dec. 31, 2017 USD ($) item	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2013 USD ($) ft²	Dec. 31, 2017 EUR (€) ft²	Dec. 31, 2017 USD ($) ft²	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Operating leases
Construction allowance	$ 5,914,000						$ 5,129,000
Facilities rent expense, net of sublease income	$ 3,500,000	$ 6,800,000	$ 6,500,000	$ 6,000,000
Minimum rental commitments under the non-cancelable operating lease agreements
2018							7,703,000
2019							7,202,000
2020							7,251,000
2021							7,074,000
2022							7,125,000
Thereafter							23,531,000
Total minimum lease payments							59,886,000
Obligations under capital leases							0
Collaborations and Licenses
Potential milestone payable							80,000,000
Manufacturing commitments
Collaborations and Licenses
Manufacturing commitment							$ 3,500,000
Reserve capacity
Collaborations and Licenses
Manufacturing commitment | €						€ 46.2
Term of agreement		5 years
Noncancelable commitment | €						€ 13.9
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
Operating lease term extension period		5 years
Construction allowance					$ 746,000			$ 186,000	$ 1,100,000
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
Area of space leased | ft²						43,850	43,850
100 River Ridge Drive, Norwood, MA
Operating leases
Area of space leased | ft²					7,507
Operating lease term extension period					5 years
Operating lease term period					5 years 2 months