Summary of Significant Accounting Policies - Product Warranty (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Product Liability Contingency [Line Items]
Standard and Extended Product Warranty Accrual	$ 2,074	$ 2,280
Summary of product warranty activity
Beginning balance	2,280	1,880
Charges to expense	1,042	1,723
Costs incurred	(1,248)	(1,323)
Ending balance	$ 2,074	$ 2,280
Minimum
Product Liability Contingency [Line Items]
Limited product warranty period	1 year
Maximum
Product Liability Contingency [Line Items]
Limited product warranty period	2 years