Property and Equipment - Property and Equipment and Related Accumulated Depreciation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 2,364	$ 2,233
Less accumulated depreciation and amortization	(1,957)	(1,747)
Total property and equipment, net	$ 407	486
Lab Equipment
Property, Plant and Equipment [Line Items]
Property and Equipment, Useful Life	5 years
Property and equipment, gross	$ 1,961	1,795
Furniture and Fixtures
Property, Plant and Equipment [Line Items]
Property and Equipment, Useful Life	4 years
Property and equipment, gross	$ 107	107
Computer Equipment
Property, Plant and Equipment [Line Items]
Property and Equipment, Useful Life	3 years
Property and equipment, gross	$ 171	206
Software
Property, Plant and Equipment [Line Items]
Property and Equipment, Useful Life	3 years
Property and equipment, gross	$ 25	25
Leasehold Improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 100	$ 100