Product Warranty (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 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	1,401	2,170
Settlements made during the period	(1,107)	(2,550)
Changes in estimate of liability for pre-existing warranties during the period	(586)	(1,155)
Balance at the end of the period	1,509	2,162
Product warranty classification
Amount classified as current	1,461	2,107	1,700
Amount classified as long-term	48	55
Total warranty liability	$ 1,509	$ 2,162