Commitments and Contingencies (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 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	(58)	(223)
Utilization of accrual	(158)	(315)
Warranty liability balance, end of the period	908	1,729
Product Warranty Accrual, Noncurrent	200		$ 200
Cash, Cash Equivalents, Restricted Cash And Restricted Cash Equivalents	11,402	$ 32,025		$ 33,087
Cash and cash equivalents	7,402		8,124
Unallocated shelf registration limit	$ 100,000
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	$ 700		$ 900