Summary of Significant Accounting Policies - Product Warranty (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Summary of product warranty activity
Beginning balance	$ 1,880	$ 1,853
Charges to expense	1,723	1,431
Costs incurred	(1,323)	(1,404)
Ending balance	$ 2,280	$ 1,880
Minimum
Product Liability Contingency [Line Items]
Limited product warranty period	1 year
Maximum
Product Liability Contingency [Line Items]
Limited product warranty period	2 years