Commitments and Contingencies - Narratives (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Class of Warrant or Right [Line Items]
Purchase Commitment, remaining minimum amount committed	$ 3,300	$ 300
Accrued warranty reserve	879	1,466
Accrued warranty reserve	$ 245	$ 355
Minimum
Class of Warrant or Right [Line Items]
Warranty, Term	12 months
Maximum
Class of Warrant or Right [Line Items]
Warranty, Term	24 months