Balance Sheet Account Detail - Schedule of Property and Equipment Net of Accumulated Depreciation (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 7,653	$ 7,450
(Less): Accumulated depreciation	(6,388)	(6,045)
Property and equipment, net of accumulated depreciation	1,265	1,405
Computer hardware and software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	3,824	3,616
Laboratory equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	609	643
Office furniture [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	348	344
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 2,872	$ 2,847