Property, Plant and Equipment - Summary of property, plant, and equipment (Details) - USD ($) $ in Thousands	Jun. 29, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 51,103	$ 43,203
Less: accumulated depreciation and amortization	16,630	12,676
Property, plant and equipment, net	34,473	30,527
Manufacturing equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	29,783	25,314
Research and development equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	7,373	6,088
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	7,337	7,080
Capital leases
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	883	882
Software
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	183	60
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	364	195
Vehicles
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	210	210
Assets not yet placed in service
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 4,970	$ 3,374