Commitments and Contingencies - Narrative (Details) $ in Thousands			1 Months Ended
	Apr. 22, 2021	Oct. 30, 2018 USD ($) shares	May 31, 2019 USD ($) licensedProduct shares	Dec. 31, 2018 USD ($)	Sep. 30, 2011 USD ($)
Commitments and contingencies
Number of licensed products | licensedProduct			1
Subsequent Event
Commitments and contingencies
Litigation stay period (in days)	10 days
Inception 4
Commitments and contingencies
Contingent consideration arrangements, maximum amount		$ 105,000
Share price calculation base, period (in days)		5 days
Contingent consideration arrangements, maximum amount (in shares) | shares		7,200,000
Contingent consideration arrangements, contingently issuable shares as a percentage of shares outstanding		19.90%
GA Product | Inception 4
Commitments and contingencies
Clinical and marketing approval milestones		$ 45,000
Wet AMD Product | Inception 4
Commitments and contingencies
Clinical and marketing approval milestones		$ 60,000
Archemix | C5 Licensed Product | Achievement of specified clinical and regulatory milestones | Maximum | License Agreements
Commitments and contingencies
Amount to be paid on achievement of milestone					$ 50,500
Archemix | C5 Licensed Product | First indication | Maximum | License Agreements
Commitments and contingencies
Amount to be paid on achievement of milestone					24,500
Archemix | C5 Licensed Product | Second and third indication | Maximum | License Agreements
Commitments and contingencies
Amount to be paid on achievement of milestone					23,500
Archemix | C5 Licensed Product | Sustained delivery applications | Maximum | License Agreements
Commitments and contingencies
Amount to be paid on achievement of milestone					2,500
Archemix | C5 Licensed Product | Achievement of specified commercial milestones | Maximum | License Agreements
Commitments and contingencies
Amount to be paid on achievement of milestone					$ 22,500
University of Florida Research Foundation (UFRF) | Specified clinical, marketing approval and reimbursement approval milestones with respect to a licensed product | RHO-adRP License Agreement
Commitments and contingencies
Amount to be paid on achievement of milestone				$ 23,500
University of Florida Research Foundation (UFRF) | Specified commercial sales milestones with respect to a licensed product | RHO-adRP License Agreement
Commitments and contingencies
Amount to be paid on achievement of milestone				$ 70,000
University Of Florida Research Foundation (UFRF) And University Of Pennsylvania (Penn) | Primary Licensed Product | Specified clinical, marketing approval and reimbursement approval milestones with respect to a licensed product | Research and Development Expense | BEST1 License Agreement
Commitments and contingencies
Payments for license fees			$ 15,700
University Of Florida Research Foundation (UFRF) And University Of Pennsylvania (Penn) | Primary Licensed Product | Specified commercial sales milestones with respect to a licensed product | Research and Development Expense | BEST1 License Agreement
Commitments and contingencies
Payments for license fees			48,000
University Of Florida Research Foundation (UFRF) And University Of Pennsylvania (Penn) | Other Licensed Product | Specified clinical, marketing approval and reimbursement approval milestones with respect to a licensed product | Research and Development Expense | BEST1 License Agreement
Commitments and contingencies
Payments for license fees			3,100
University Of Florida Research Foundation (UFRF) And University Of Pennsylvania (Penn) | Other Licensed Product | Specified commercial sales milestones with respect to a licensed product | Research and Development Expense | BEST1 License Agreement
Commitments and contingencies
Payments for license fees			9,600
University Of Massachusetts (UMass) | miniCEP290 | Achievement of specified clinical and regulatory milestones | License Agreements | Research and Development Expense
Commitments and contingencies
Payments for license fees			$ 14,750
Shares issued for license fees (in shares) | shares			75,000
University Of Massachusetts (UMass) | miniCEP290 | Specified commercial sales milestones with respect to a licensed product | License Agreements | Research and Development Expense
Commitments and contingencies
Payments for license fees			$ 48,000