Collaborative and other licensing arrangements (Collaborative Arrangements) (Details) € in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2016 EUR (€)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 EUR (€)
In-licensing arrangements
Option exercise fee, for each protein | €						€ 20.0
Agreement with SFJ Pharmaceuticals IX, L.P. [Member]
In-licensing arrangements
Maximum conditional obligation	$ 451.5		$ 451.5
Fair value of assumed contingency	(288.6)		(288.6)
Business collaboration development cost funding	165.0		165.0
Option to increase R&D funding	35.0		35.0
Unfunded Contingent Payments [Member]
Unfunded Contingent Payments [Abstract]
Unfunded Contingent Payments			1,800.0
In-licensing Arrangement | Collaboration with Precision BioSciences [Member] | Future payments related to option fees and development, regulatory and commercial milestones
In-licensing arrangements
Maximum conditional obligation	1,600.0		1,600.0
In-licensing Arrangement | Research Collaboration with Symphogen [Member] | Future payments related to option fees and development, regulatory and commercial milestones
In-licensing arrangements
Milestones payment | €				€ 1,200.0
Out-licensing Arrangement
Out-licensing arrangements
Milestone payments received			0.5		$ 12.6
Milestone revenues recognized			2.3		1.0
Out-licensing Arrangement | Other Revenues
Out-licensing arrangements
Milestone revenues recognized	1.0	$ 0.5
Out-licensing Arrangement | Product Sales
Out-licensing arrangements
Milestone revenues recognized	16.2	$ 14.2	31.3		$ 23.4
Out-licensing Arrangement | Development Milestone
Out-licensing arrangements
Maximum milestone payment receivable	32.0		32.0
Out-licensing Arrangement | Sales Milestone
Out-licensing arrangements
Maximum milestone payment receivable	$ 42.7		42.7
Out-licensing Arrangement | License Agreement with Merrimack Pharmaceuticals [Member] | Future payments related to option fees and development, regulatory and commercial milestones
In-licensing arrangements
Milestones payment			678.0
Out-licensing Arrangement | License Agreement with Coherus Biosciences, Inc [Member] | Future payments related to option fees and development, regulatory and commercial milestones
In-licensing arrangements
Milestones payment			$ 70.0