Property, Plant and Equipment - Summary of Property, Plant and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Property Plant And Equipment [Line Items]
Less: accumulated depreciation and amortization	$ (13,544)	$ (14,151)
Property, plant and equipment, net	2,476	1,879
Research Equipment [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment	6,815	6,356
Office Furniture and Equipment [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment	980	1,069
Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment	1,887	1,780
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment	$ 6,338	$ 6,825