Collaboration Agreements (Ang2 Antibody and PDGFR-beta Antibody) (Details) - USD ($) $ in Thousands		3 Months Ended
	Mar. 31, 2016	Mar. 31, 2014	Dec. 31, 2017	Dec. 31, 2016
Collaboration Agreements [Line Items]
Accounts receivable from Bayer			$ 242,014	$ 175,263
PDGFR-beta outside the US
Collaboration Agreements [Line Items]
Maximum percentage of outstanding shares that may be acquired, under 'standstill' provisions			20.00%
Percentage of global development cost to be paid by the collaboration partner under the collaboration	25.00%
Percentage of development cost for the territory outside the United States to be paid for under the collaboration	50.00%
Deferred Revenue, Additions		$ 25,500
Ang2 Antibody [Member]
Collaboration Agreements [Line Items]
Percentage of global development cost to be paid by the collaboration partner under the collaboration	25.00%
Percentage of development cost for the territory outside the United States to be paid for under the collaboration	50.00%
Deferred Revenue, Additions	$ 50,000
Recognition of Deferred Revenue	$ 37,400