Balance Sheet Account Detail - Schedule of Property and Equipment Net of Accumulated Depreciation (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 7,569	$ 7,450
(Less): Accumulated depreciation	(6,256)	(6,045)
Property and equipment, net of accumulated depreciation	1,313	1,405
Computer hardware and software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	3,705	3,616
Laboratory equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	657	643
Office furniture [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	347	344
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 2,860	$ 2,847