Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued Liabilities [Abstract]
Salaries, employee benefits and related taxes	$ 1,758	$ 1,389
Retention payments	0	2,233
CIRM upfront funding - current	2,583	2,446
Other	516	1,743
Accrued liabilities	$ 4,857	$ 7,811