Property and Equipment - Components of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 5,276	$ 5,425
Less accumulated depreciation and amortization	(4,867)	(4,802)
Total	409	623
Furniture, Fixtures and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	961	1,000
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,471	1,411
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 2,844	$ 3,014