Property, Plant and Equipment - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Less: accumulated depreciation and amortization	$ (14,690)	$ (16,199)
Net book value	1,660	991
Research Equipment [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment	6,522	7,313
Office Furniture and Equipment [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment	985	1,046
Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment	2,473	2,461
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment	$ 6,370	$ 6,370