Collaboration arrangements and concentration of credit risk - Revenues (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Collaboration arrangements
Revenues	$ 25,098	$ 10,578	$ 6,141
Collaboration arrangement
Collaboration arrangements
Revenues	25,098	10,578	6,141
Collaboration arrangement \| BMS
Collaboration arrangements
Revenues	16,959	4,677
Collaboration arrangement \| Chiesi Farmaceuticai S.p.A
Collaboration arrangements
Revenues	$ 8,139	$ 5,901	$ 6,141

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Name:	us-gaap_Revenues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration