Astellas (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended	12 Months Ended	96 Months Ended
	Aug. 31, 2010	Mar. 31, 2007	Mar. 31, 2015	Dec. 31, 2017	Jul. 01, 2018
License Agreement with Astellas Pharma Inc.
Deferred Revenue Arrangement [Line Items]
Non-exclusive license agreement term		6 years
Advance payment received due to amended licensing agreement	$ 165.0
Future payment to be made under terms of amended licensing agreement				$ 130.0
Number of days of advance written notice to terminate agreement				90 days
Aflibercept Agreement [Member]
Deferred Revenue Arrangement [Line Items]
Deferred Revenue, Revenue Recognized			$ 14.9
Scenario, Forecast [Member] | License Agreement with Astellas Pharma Inc.
Deferred Revenue Arrangement [Line Items]
Recognition period for advance payment					7 years