Share capital - Warrants (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Aug. 20, 2013	Aug. 18, 2013
Class of Warrant or Right [Line Items]
Maximum percent of warrants reserved for issuance	4.00%
Maximum value of warrants reserved for issuance	$ 1,000,000,000
Exercise price (in dollars per share)	10.00
Authorized and issued (in shares)	4,651,163.000
Aggregated fair value of warrants	17,374,000
Warrants authorized and issued (in shares)		1,003,157	3,648,006
Term of warrants	10 years
Founders
Class of Warrant or Right [Line Items]
Maximum percent of warrants reserved for issuance	3.50%
Exercise price (in dollars per share)	10.00
Authorized and issued (in shares)	4,069,768
Aggregated fair value of warrants	15,203,000
Advisor
Class of Warrant or Right [Line Items]
Maximum percent of warrants reserved for issuance	0.50%
Exercise price (in dollars per share)	10.00
Authorized and issued (in shares)	581,395
Aggregated fair value of warrants	$ 2,171,000