Commitments and contingencies (Details)	9 Months Ended
	Sep. 30, 2016 USD ($) Plaintiff Complaint shares	May 25, 2016 USD ($)	Feb. 26, 2016 Motion	Dec. 31, 2015 USD ($) shares
Loss Contingencies [Line Items]
Amount of milestone payment payable	$ 7,500,000
Potential future milestone payments on each additional final marketing approval	$ 1,000,000
Number of plaintiffs | Plaintiff	2
Number of competing derivative complaints | Complaint	2
Litigation settlement due in shares	$ 0	$ 4,500,000		$ 4,500,000
Common stock issued (in shares) | shares	96,943,072			66,480,065
Number of motions filed by the company | Motion			2
Litigation settlement due in shares of common [Member]
Loss Contingencies [Line Items]
Litigation settlement due in shares				$ 4,500,000