Balance Sheet Account Detail - Schedule of Property and Equipment Net of Accumulated Depreciation (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 6,435	$ 6,295
(Less): Accumulated depreciation	(5,942)	(5,846)
Property and equipment, net of accumulated depreciation	493	449
Computer hardware and software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	2,684	2,550
Laboratory equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	622	622
Office furniture [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	217	211
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 2,912	$ 2,912