Commitments and Contingencies (Collaborative Arrangements) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
In-licensing Arrangement | Research Collaboration with Santaris
In-licensing arrangements
Milestones payment	$ 0	$ 1.5	$ 3.0
Support costs	0.4	4.5	8.1
In-licensing Arrangement | Collaboration and Licensse Agreement with Sangamo
In-licensing arrangements
Upfront payment			13.0
Maximum conditional obligation	213.5
Milestones payment	1.0	0	0
Support costs	22.6	15.2	8.9
In-licensing Arrangement | Stategic licensing and collaboration agreement ArmaGen
In-licensing arrangements
Upfront payment	15.0
Maximum conditional obligation	208.0
Share of R&D costs recorded within R&D expense	1.7
Out-licensing Arrangement
Out-licensing arrangements
Milestone payments received	2.2	3.0	18.3
Out-licensing Arrangement | Other Revenues
Out-licensing arrangements
Milestone revenues recognized	16.7	5.0	19.4
Out-licensing Arrangement | Product Sales
Out-licensing arrangements
Milestone revenues recognized	46.5	58.3	83.8
Out-licensing Arrangement | Development Milestone
Out-licensing arrangements
Maximum milestone payment receivable	39.0
Out-licensing Arrangement | Sales Milestone
Out-licensing arrangements
Maximum milestone payment receivable	$ 59.0