Product Warranty (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Product Warranty
Product warranty period	1 year
Changes in standard product warranty liability
Balance at the beginning of the period	$ 2,666	$ 3,555
Warranties issued during the period	2,577	1,551
Settlements made during the period	(1,090)	(2,399)
Changes in estimate of liability for pre-existing warranties during the period	(281)	520
Balance at the end of the period	3,872	3,227
Product warranty classification
Amount classified as current			$ 3,537	$ 2,426	$ 2,958
Amount classified as long-term			335		269
Total warranty liability	$ 2,666	$ 3,555	$ 3,872	$ 2,666	$ 3,227