Product Warranty (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Product Warranty
Product warranty period	1 year
Changes in product warranty liability
Balance at the beginning of the period	$ 3,697	$ 2,713	$ 726
Warranties issued during the period	3,042	4,772	3,722
Settlements made during the period	(3,010)	(5,275)	(1,923)
Changes in estimate of liability for pre-existing warranties during the period	(1,928)	1,487	188
Balance at the end of the period	1,801	3,697	2,713
Product warranty classification
Amount classified as current	1,700	3,556	2,556
Amount classified as long-term	101	141	157
Total Warranty liability	$ 1,801	$ 3,697	$ 2,713