401(k) savings plan (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Savings Plan - 401(k) [Member]
Defined Benefit Plan Disclosure [Line Items]      
Contributions to 401(k) $ 53 $ 48 $ 43