Balance Sheet Account Detail - Schedule of Property and Equipment Net of Accumulated Depreciation (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 7,680	$ 7,620
(Less): Accumulated depreciation	(7,037)	(6,702)
Property and equipment, net of accumulated depreciation	643	918
Computer hardware and software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	3,823	3,785
Laboratory equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	622	608
Office furniture [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	355	355
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 2,880	$ 2,872