Balance Sheet Account Detail - Schedule of Property and Equipment Net of Accumulated Depreciation (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 6,928	$ 6,883
(Less): Accumulated depreciation	(6,462)	(6,498)
Property and equipment, net of accumulated depreciation	466	385
Computer hardware and software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	3,075	3,079
Laboratory equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	669	635
Office furniture [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	227	212
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 2,957	$ 2,957