Selected Balance Sheet Information (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Other Current Assets [Line Items]
Prepaid clinical research organizations	$ 1,677	$ 8,329
Prepaid insurances	358	339
Other prepaid expenses	295	208
Other receivables	185	0
Intrexon prepaid research and development expenses	0	643
Total	$ 2,515	$ 9,519