Property, Plant and Equipment - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property Plant And Equipment [Line Items]
Less: accumulated depreciation and amortization	$ (15,083)	$ (14,582)
Net book value	1,404	1,989
Research Equipment [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment	6,789	6,925
Office Furniture and Equipment [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment	1,045	1,040
Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment	2,283	2,236
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment	$ 6,370	$ 6,370