Product Warranty (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Product Warranty
Product warranty period	1 year
Changes in product warranty liability
Balance at the beginning of the period	$ 1,428	$ 1,801
Warranties issued during the period	1,028	1,401
Settlements made during the period	(1,511)	(1,107)
Changes in estimate of liability for pre-existing warranties during the period	264	(586)
Balance at the end of the period	1,209	1,509
Product warranty classification
Amount classified as current	1,160	1,461	1,316
Amount classified as long-term	49	48
Total Warranty liability	$ 1,209	$ 1,509