Property and Equipment, net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Less - accumulated depreciation	$ (13,155)	$ (15,028)
Property and equipment, net	1,911	3,001
Depreciation	811	1,224	$ 601
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	8,864	10,135
Software, office and computer equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	2,487	3,115
Furniture, fixtures and fittings
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 3,715	$ 4,779