Supplemental Balance Sheet Information - Standard Product Warranty Liability (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Movement in Standard Product Warranty Accrual [Roll Forward]
Accrued warranty balance	$ 7,661	$ 8,104
Accrued warranty, net	3,343	7,058
Warranty expenditures during period	(1,982)	(7,501)
Accrued warranty balance	$ 9,022	$ 7,661