Property, Plant and Equipment, net - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Impairment charges of property, plant and equipment	$ 0	$ 88,000
Property, plant and equipment, gross	9,842,000	8,460,000
Accumulated depreciation and amortization	8,090,000	6,700,000
Depreciation expense on property, plant and equipment	1,400,000	$ 1,300,000
Assets Under Capital Lease
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	500,000
Accumulated depreciation and amortization	$ 200,000