Product Warranty (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Product Warranty
Product warranty period	1 year
Changes in product warranty liability
Balance at the beginning of the period	$ 1,801	$ 3,697
Warranties issued during the period	457	842
Settlements made during the period	(399)	(1,078)
Changes in estimate of liability for pre-existing warranties during the period	(277)	(225)
Balance at the end of the period	1,582	3,236
Product warranty classification
Amount classified as current	1,539	3,110	1,700
Amount classified as long-term	43	126
Total warranty liability	$ 1,582	$ 3,236