Accrued Expenses (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Accrued Expenses
Technology access fee payable to Intrexon (present value)	$ 2,186
Compensation and related benefits	719	471
Legal, audit and tax services	605	330
Preclinical, clinical and contract manufacturing	258	93
Consulting	174	139
Other expenses	178	178
Accrued expenses	$ 4,120	$ 1,211