Commitments and contingencies - Other Agreements - (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) item	Dec. 31, 2014 USD ($) item
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of additional disease indications for which the Company has options to license intellectual property | item	4
Aggregate maximum milestone payments to be paid to collaborative partner	$ 12,000,000
Aggregate upfront fees to be paid to collaborative partner	$ 1,500,000
Number of milestones achieved | item	0	0
Patent costs incurred	$ 872,000	$ 295,000
Loss Contingency [Abstract]
Contingency reserves for litigation liabilities	0
Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Per Milestone and per disease indication, maximum milestone payments to be paid to collaborative partner	$ 5,000,000
Number of days written notice required by reporting entity to terminate agreement	30 days
Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Per Milestone and per disease indication, maximum milestone payments to be paid to collaborative partner	$ 20,000,000
Number of days written notice required by reporting entity to terminate agreement	90 days
Various contract research organizations and institutions | Research and development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Payments of upfront license fees	$ 830,000	$ 75,000