Commitments and Contingencies (Details) $ in Millions	Jun. 30, 2018 USD ($)
License Agreements | Archemix | C5 Licensed Product | Achievement of specified clinical and regulatory milestones | Maximum
Commitments and contingencies
Amount to be paid on achievement of milestone	$ 57.5
License Agreements | Archemix | C5 Licensed Product | First indication | Maximum
Commitments and contingencies
Amount to be paid on achievement of milestone	30.5
License Agreements | Archemix | C5 Licensed Product | Second and third indication | Maximum
Commitments and contingencies
Amount to be paid on achievement of milestone	24.5
License Agreements | Archemix | C5 Licensed Product | Sustained delivery applications | Maximum
Commitments and contingencies
Amount to be paid on achievement of milestone	2.5
License Agreements | Archemix | C5 Licensed Product | Achievement of specified commercial milestones | Maximum
Commitments and contingencies
Amount to be paid on achievement of milestone	22.5
RHO-adRP License Agreement | University of Florida Research Foundation (UFRF) | Specified clinical, marketing approval and reimbursement approval milestones with respect to a licensed product
Commitments and contingencies
Amount to be paid on achievement of milestone	23.5
RHO-adRP License Agreement | University of Florida Research Foundation (UFRF) | Specified commercial sales milestones with respect to a licensed product
Commitments and contingencies
Amount to be paid on achievement of milestone	$ 70.0