Product Warranty (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 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	1,166	921
Settlements made during the period	(454)	(1,306)
Changes in estimate of liability for pre-existing warranties during the period	(254)	365
Balance at the end of the period	3,124	3,535
Product warranty classification
Amount classified as current			$ 2,748	$ 2,426	$ 3,288
Amount classified as long-term			376		247
Total warranty liability	$ 2,666	$ 3,555	$ 3,124	$ 2,666	$ 3,535