Property and Equipment - Net Property and Equipment at Cost (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment
Total property and equipment, at cost	$ 5,798	$ 5,146
Less: accumulated depreciation and amortization	3,945	3,454
Property and equipment, net	1,853	1,692
Leasehold improvements
Property, Plant and Equipment
Total property and equipment, at cost	671	603
Laboratory equipment and other
Property, Plant and Equipment
Total property and equipment, at cost	$ 5,127	$ 4,543