Investments in Variable Interest Entities (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Oct. 31, 2017	Sep. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity [Line Items]
Payment to Neurimmune			$ 134.1	$ 0.0	$ 56.1
Investment in Variable Interest Entities (Textual)
Investment in biotechnology companies that are determined to be unconsolidated variable interest entities			48.3	$ 47.4
Neurimmune
Variable Interest Entity [Line Items]
Payment to Neurimmune	$ 150.0	$ 60.0
Reduction in royalty rate payable on commercial sales	15.00%
Additional reduction in royalty rate payable on commercial sales	5.00%
Additional potential payment to Neurimmune	$ 50.0
Investment in Variable Interest Entities (Textual)
Remaining potential development milestone payments and royalties on commercial sales under the terms of collaboration agreement			$ 275.0