Property and Equipment (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Property and Equipment, Gross	$ 9,676	$ 9,929
Less: accumulated depreciation and amortization	(7,883)	(7,564)
Property and equipment, net	1,793	2,365
Depreciation expense	593	717
Furniture and office equipment
Property Plant And Equipment [Line Items]
Property and Equipment, Gross	4,445	4,552
Leasehold improvements
Property Plant And Equipment [Line Items]
Property and Equipment, Gross	5,168	5,168
Lab equipment
Property Plant And Equipment [Line Items]
Property and Equipment, Gross	$ 63	$ 209

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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The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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