Collaborative and other licensing arrangements (Narrative) (Details) € in Millions	1 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($)	Jul. 31, 2016 USD ($)	Jun. 30, 2016	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2016 EUR (€)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 EUR (€)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Option exercise fee, for each protein | €									€ 20
Out-licensing Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments received				$ 3,000,000	$ 0	$ 3,500,000		$ 12,600,000
Development Milestone | Out-licensing Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum milestone payment receivable	$ 17,300,000			17,300,000		17,300,000
Sales Milestone | Out-licensing Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum milestone payment receivable	17,700,000			17,700,000		17,700,000
Other Revenues | Out-licensing Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone revenues recognized				1,700,000	500,000	4,000,000		1,500,000
Product Sales | Out-licensing Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone revenues recognized				16,400,000	$ 13,800,000	47,700,000		$ 37,200,000
Agreement with SFJ Pharmaceuticals IX, L.P.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Fair value of assumed contingency	288,600,000			288,600,000		288,600,000
Collaboration with Precision BioSciences | Future payments related to option fees and development, regulatory and commercial milestones | In-licensing Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum conditional obligation	1,600,000,000.0			$ 1,600,000,000.0		1,600,000,000.0
Research Collaboration with Symphogen | Future payments related to option fees and development, regulatory and commercial milestones | In-licensing Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestones payment | €							€ 1,200
License Agreement with Merrimack Pharmaceuticals | Future payments related to option fees and development, regulatory and commercial milestones | Out-licensing Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestones payment						$ 678,000,000
Pfizer Inc [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment		$ 90,000,000
SFJ Pharmaceuticals Group [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payments to terminate agreement	$ 288,000,000
Minimum | Pfizer Inc [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestones payment		75,000,000
Maximum | Pfizer Inc [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestones payment		$ 460,000,000
Baxalta | Option to Obtain Exclusive Licensing Rights
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Exercise period after protein is ready for Phase 2 clinical trials			90 days