Property and Equipment - Composition of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,978	$ 1,947
Less accumulated depreciation	(1,727)	(1,645)
Property and equipment, net	251	302
Lab Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,684	1,681
Computer Hardware, Software and Telephone
Property Plant And Equipment [Line Items]
Property and equipment, gross	200	174
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	70	70
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 24	$ 22

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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