Commitments and Contingencies (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Movement in Standard Product Warranty Accrual [Roll Forward]
Warranty liability balance, beginning of the period	$ 1,124	$ 1,821
Product warranty accruals	238	305
Utilization of accrual	(331)	(1,002)
Warranty liability balance, end of the period	1,031	1,124
Product Warranty Accrual, Noncurrent	400	200
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	14,094		$ 12,682	$ 33,087
Unallocated shelf registration limit	$ 14,000
Minimum
Product Warranty Liability [Line Items]
Warranty, Term	12 months
Maximum
Product Warranty Liability [Line Items]
Warranty, Term	24 months
Other Accrued Liabilities [Member]
Movement in Standard Product Warranty Accrual [Roll Forward]
Product Warranty Accrual, Current	$ 600	$ 900