Related-party transactions (Details) (Consulting Agreement [Member], USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2013
Scientific Advisor [Member]
Dec. 31, 2011
Scientific Advisor [Member]
Related Party Transaction [Line Items]      
Related party consulting agreement, general and administrative expense $ 302 $ 302 $ 302