Fair value (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets measured at fair value
Cash and Cash Equivalents	$ 10,014	$ 8,896
Restricted Cash	375	375
Short term investments	6,191	907
Total Assets measured at fair value	16,580	10,178
Liabilities measured at fair value
Preferred Stock Warrant Liability		(109)
Total Liabilities measured at fair value		(109)
Fair Value, Inputs, Level 1 [Member]
Assets measured at fair value
Cash and Cash Equivalents	10,014	8,896
Restricted Cash	375	375
Short term investments	0	0
Total Assets measured at fair value	10,389	9,271
Liabilities measured at fair value
Preferred Stock Warrant Liability		0
Total Liabilities measured at fair value		0
Fair Value, Inputs, Level 2 [Member]
Assets measured at fair value
Cash and Cash Equivalents	0	0
Restricted Cash	0	0
Short term investments	6,191	907
Total Assets measured at fair value	6,191	907
Liabilities measured at fair value
Preferred Stock Warrant Liability		0
Total Liabilities measured at fair value		0
Fair Value, Inputs, Level 3 [Member]
Assets measured at fair value
Cash and Cash Equivalents	0	0
Restricted Cash	0	0
Short term investments	0	0
Total Assets measured at fair value	0	0
Liabilities measured at fair value
Preferred Stock Warrant Liability	0	(109)	0
Total Liabilities measured at fair value		$ (109)