Accrued Liabilities - Activity Related to Accrued Warranties (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Standard Product Warranty Accrual [Roll Forward]
Beginning Balance	$ 2,594	$ 2,309	$ 2,719
Provision for warranty expense	4,045	3,544	3,597
Fulfillment of warranty obligations	(4,011)	(3,259)	(4,007)
Ending Balance	$ 2,628	$ 2,594	$ 2,309