Property and Equipment - Property and Equipment and Related Accumulated Depreciation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 867	$ 2,364
Less accumulated depreciation and amortization	(71)	(1,957)
Total property and equipment, net	$ 796	407
Lab equipment
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	5 years
Property and equipment, gross	$ 457	1,961
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	4 years
Property and equipment, gross	$ 16	107
Computer equipment
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	3 years
Property and equipment, gross	$ 73	171
Software
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	3 years
Property and equipment, gross	$ 28	25
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 293	$ 100