Product Warranty (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Product Warranty
Product warranty period	1 year
Changes in product warranty liability
Balance at the beginning of the period	$ 1,801	$ 3,697	$ 2,713
Warranties issued during the period	2,240	3,042	4,772
Settlements made during the period	(1,515)	(3,010)	(5,275)
Changes in estimate of liability for pre-existing warranties during the period	(1,098)	(1,928)	1,487
Balance at the end of the period	1,428	1,801	3,697
Product warranty classification
Amount classified as current	1,316	1,700	3,556
Amount classified as long-term	112	101	141
Total Warranty liability	$ 1,428	$ 1,801	$ 3,697